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a priori-a posteriori distinctions
an epistemological distinction. A priori propositions, unlike a posteriori propositions, do not require to establish their truth. We derive or justify a priori concepts, unlike a posteriori concepts, independent of experience.

abstract ideas
Locke's attempt, rejected by Berkeley, to explain how an idea can stand for individuals of a given kind, even though the individuals vary in their properties. Locke held that abstraction from different properties would produce a general idea covering the right individuals.

abstract objects
objects, such as numbers or universals, that do not exist as spatio-temporal particulars. Philosophers disagree about whether there can be such objects or, if they do exist, how they are related to concrete physical objects.

ad hominem argument
a fallacious argument attacking the holder of a view rather than the position itself or a sound argument showing an inconsistency between a view held by a person and a consequence of that view. The person pointing out the inconsistency need not hold the initial view.

alientation/estrangement
Hegelian concept, also used by Marx and later European philosophers, to stand for a state of being cut off from something of importance, such as oneself, others, nature or the product of one's labour. The analysis and interpretation of alienation varies according to the philosopher.

altruism
the view that the well-being of others should have as much importance for us as the well-being of ourselves. Some argue that altruism, even if it is desirable, is not possible, and that our ethics must be based on egoism.

analysis
the central method of analytical philosophy, shaped by the development of modern logic and found in the work of Frege, Russell, Moore and Wittgenstein, according to which philosophical problems can be overcome through replacing the apparent structure of statements by their real logical structure. Many philosophers, while still considering themselves analytical philosophers, have altered or even abandoned this programme.

analytic-synthetic distinction
According to Kant's formulation of the distinction, in an analytic proposition the concept of the predicate is contained in the concept of the subject, and we can tell that the proposition is true by analysis. In a synthetic proposition, the concept of the predicated adds something new to the concept of the subject, and the truth or falsity of the proposition cannot be determined by analysis. There has been much dispute over the adequacy of this account, but there is general agreement that synthetic propositions tell us something about the world. Together with the metaphysical distinction between necessary and contingent propositions and the epistemological distinction between a priori and a posteriori propositions, this logical distinction sets the framework for much modern philosophy. Kant famously argued that some a priori necessary propositions are synthetic. Contemporary discussion has developed from Quine's criticism of the distinction as a dogma of empiricism.

aporia
a puzzle or perplexity. In the early Platonic dialogues, Socrates raised problems without offering solutions to them and showed that those he questioned could not offer an acceptable solution either. The aporetic method let to the development of the dialectical methold, by which Socrates elicited truth through questioning. The term aporia (no way through) was introduced by Aristotle for puzzles concerning incompatibilities that arise among views we hold without prompting or among reputable beliefs adopted commonly or by the wise. His approach was to seek the minimal adjustments needed to reconcile these conflicting views.

argument from design
the argument for the existence of God, disputed by Hume, according to which the complex and intricate order of the world can only be explained (or can best be explained) by positing an intelligent and powerful creator.

artificial intelligence (AI)
the use of programs to enable machines to perform tasks which humans perform using their intelligence. Early AI avoided human pychological models, but this orientation has been altered by the development of connectionism, which is based on theories of how the brain works. In connectionism, complex functions, including learning, involve the transmission of information along pathways formed among large arrays of simple elements. AI raised questions about the conditions, if any, in which we would be justified in ascribing mental attributes to purely physical systems.

association of ideas
a view, especially important to Hume, explaining the patterned occurrence of out ideas according to laws of assocation. Philosophers today generally seek to maintain what is important in Hume while rejecting this mechanism.

autonomy
an autonomous being is one that has the power of self-direction, possessing the ability to act as it decides, independent of the will of others and of other internal or external factors.

axioms
propositions selected as the foundations of a field - classically geometry - which, together with methods of proof, allow other propositions to be proved in an ordered way. The axiomatic method has powerfully influenced philosophy, although each feature of the method has been criticized as inappropriate for philosophy.

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Categorical Imperative
the fundamental formal demand (or set of demands) which Kant place on our choice of principles on which to act. It is contrasted with hypothetical imperatives, which have force only if we have certain desires or inclinations. Formulations of the categorical imperative seem to be radically different from one another, and some critics argure that the categorical imperative produces an empty formalism. Sympathetic commentators believe that both these problems can be overcome. The formulations test the principles on which we act according to whether they can be universal laws or laws of nature, whether we treat humanity in ourselves and others never simply as means by also as ends, whether we treat every rational being as a will making universal law, and whether we treat our shared moral life as taking place within a kingdom of ends. None of the principal notions used in expressing the Categorical Imperative is easy to understand.

categories
the basic general concepts of thought, language or reality, sometimes claimed to have an origin or justification differing from those of ordinary concepts. Aristotle and Kant provide the classical discussions of categories, although categories play different roles in their thought.

category mistake
an ascription of something to one category when it belongs to another. For Ryle, who introduced the term, discriminations among categories were not confined to the great Aristotelian or Kantian categories, although categories play different roles in their thought.

causal theory of reference
the view of Kripke and others that names, and perhaps some other terms, gain meaning from an initial act of naming and then preserve meaning through suitable causal links.

causation
In causal relations between events, if an event of the first kind occurs, an event of the second kind will or must occur, and the first event will explain the occurence of the second event. Possibly items other that events can enter into causal relations. Since Hume, we have been puzzled about whether causal relations are real or are just matters of our imposing our habits upon the world and over the nature of causal necessity.

certainty
Descartes sought to build knowledge on the basis of certainty, with no room for doubt. Although the project as a whole, as well as its detail, has been contested, certainty remains an ideal for many philosophers.

chaos theory
the theory of non-linear functions, such that small differences in the input of the function can result in large and unpredictable differences in the output.

class
a collection of entities satisfying a condition for membership in the class. To avoid problems arising if classes get too large, or belong to other classes, or are not completed, set theory distinguishes classes from sets.

clearness and distinctness
Descartes' criteria of indubitable truth derived from his reflection on the impossibility of doubting his own existence (see cogito ergo sum). Clear perceptions are 'present and accessible'. Distinct perceptions are 'sharply separated' from other perceptions and contain only what is clear. We can hope to specify clearness and distinctness in an illuminating way, but this might involve replacing perceptual characterizations by conceptual ones.

cogito ergo sum
Descartes' crucial claim 'I think therefore I am' provides a standard of certainty for the rest of his philosophy and leads on to the claim that what he is is a thinking thing.

concept
'concept' can be taken psychologically or logically for what we grasp in understanding an expression, but since Frege the logical side has had primary importance. For Frege, there was a crucial distinction between objects (referred to by names or subjects) and concepts (referred to by predicates). Different accounts of logical form might challenge this claim. If concepts are thought of as components of propositions, scepticism about propositions can produce scepticism about concepts as well.

consciousness
a philosophical explanation of what consciousness is or how it might be explained eludes us. If we stick to what it is like to be a conscious human being, we have no explanation; if we try to explain consciousness in terms of what goes on in our brains, the sheer feel of consciousness itself is left aside.

consent
from Locke, the liberal theory of government has required the consent of the governed for political rule to be legitimate. Because explicit consent is not always available, Locke introduced a notion of tacit consent, but it is not always easy to distinguish tacit consent from non-consent to determine whether tacit consent is consent.

Consequentialism
the view that the value of an action is determined by the value of its consequences rather than by the principle on which the action is performed or the virtue it expresses. Utilitarianism is a consequentialist theory, where the relevant value is individual happiness or well-being.

conservative
in politics, a loosely defined term indicating adherence to one or more of a family of attitudes, including respect for tradition and authority and resistance to wholesale or sudden changes.

consistency
propositions are consistent if they can all be true. A system of propositions can be shown to be inconsistent if it contains a contradiction (a proposition and its negation). Consistency and completeness are two key concerns of modern logic.

constructivism
in the philosophy of mathematics, a broad position (encompassing both intuitionism and formalism but also going beyond them) which holds that mathematical entities exist only if they can be constructed and that proof and truth in mathematics are co-extensive. Constructivists oppose the realist (or Platonist) view that mathematical objects or truth exist independently of human procedures. This has the consequence that certain classical results whose proof rely on Platonic assumptions are not constructively valid.

contents of consciousness
mental states, like statements and other linguistic items, have contents, but it is a philosophical problem how this can be so. Furthermore, there are disputes over the extent to which internal factors and external environmental factors respectively contribute to determining the contents of mental states.

contingent-necessary distinction
contingent propositions happen to be true or false but could be otherwise. Necessary propositions must be true. It is not clear that there are any necessary propositions or, if there are, that they are restricted to analytic propositions or other propositions true because of their logical form. A contingent event is one that does not necessarily take place. If there are necessary events, natural rather than logical necessity is involved.

continuum
a collection of points, such that between any two points there are distinct points. Classical examples of a continuum are a line, plane or space.

continuum hypothesis
the claim that there are only two classes into which any thinkable collection of infinitely many distinct real numbers may fall.

contradiction
a conjunction of a proposition and its negation, which, according to the principle of non-contradiction, cannot be true. Aristotle pointed out the dangers of accepting contradictions. Except in some specially designed logics, anything can follow from a contradiction.

conventialism
the view that human conventions rather than independent realities or necessities shape our basic concepts of the world, scientific theories, ethical principles and the like. On this view, we could have chosen other conventions, which would have been as satisfactory as the conventions entrenched in our actual account of the world or morality. Some conventionalist positions allow for a contribution by reality as well as by conventions, but it is difficult to distinguish these contributions.

counterfactual conditional
a conditional (if p, then q) in which the 'if clause' is contrary to fact; for example, 'if the water had been boiling, you would have been scalded'. There is no generally satisfactory analysis of counterfactual conditionals, although some philosophers believe that we need them to deal with many important philosophical problems.

criterion
a test or standard by which truth, existence, identity or meaning can be determined. Questions arise over the choice of criteria and over the relation between criteria and that for which they are criteria.

critique
Kant introduced the term for the critical examination of reason by itself. Later European philosophers have pursued a method of critique, but some have relinquished Kant's commitment to reason as the key element of their reflective method.

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Dasein
in Heidegger's pursuit of what he considered to be the central question in philosophy - that is, the question of the meaning of Being - he spoke of our Being as human beings as Dasein (being there). In talking of ourselves in this way, he meant Dasein to break with the whole history of ontology, including the inherited Cartesian conception of the self, and to replace it with a new orientation.

deconstruction
Derrida's method aiming to overcome crucial metaphysical dichotomies. By showing that one term of an opposition is unjustifiably privileged with respect to the other, deconstruction allows us to use the pair of terms freed from metaphysical distortion. His approach to deconstruction employs sophisticated and surprising responses to language, culture and society derived from Freud and others.

defeasible
the standard criteria for the correct application of a defeasible concept allow for that application to be retracted in the light of further evidence. Verification of claims using defeasible concepts is never conclusive, in principle being always open to revision. For example, in epistemology, a defeasible knowledge claim is one made confidently, but in recognition of the possibility (no matter how apparently unlikely) that further evidence could give reason for the claim to be withdrawn.

definite description
a description picking out something as the sole individual having a certain property. Russell's theory of definite descriptions analyses sentences containing definite descriptions to remove the burden of finding objects to which these expressions seem to refer.

deontology
an ethics based on acting according to duty or doing what is right, rather than on achieving virtue or on bringing about good consequences. It is too crude to make sharp divisions or to deny a place for more than one approach to ethics. Kant is the most important deontological theorist.

dialectic
the Socratic method of discovering truth through questioning and debate, altered and developed by his Greek successors, and still a model of overwhelming importance in philosophy. Kantian dialectic expressed reason's capacity to reach contradictory conclusions from apparently sound premises. Hegel's dialectic drove the necessary unfolding and development of concepts in history. Marx's dialectic explained the historical development of society through class conflict and the relations between the forces and relations of production and the base and superstructure.

didactic
offered with the intention of instruction or teaching.

dualism
the view that each person is two entities, a mind with mental attributes and a body with physical attributes, instead of a single entity with attributes of both sorts.

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egoism
the view that we are always motivated by self-interest or that we always should be so motivated. Contemporary rational choice theorists attempt to understand how actual social institutions can be based on the choices of individuals acting according to egoist principles. The prisoner's dilemma and other problem cases show difficulties with this approach.

eliminative materialism
the view that our mental concepts, such as belief and desire, are inappropriate for a serious scientific account of human beings and should, or will be, eliminated.

empiricism
the claim that all knowledge or all meaningful discourse about the world is related to sensory experience or observation. Logical empiricism (or logical positivism) combined modern logical analysis with the demands of empiricism and was most famous for its verificationist theory of meaning.

Enlightenment
broad intellectual movement in eighteenth-century Europe, particularly Britain, France and Germany, characterized by a rejection of superstition and mystery and an optimism concerning the power of human reasoning and scientific endeavour (hence its alternative name: The Age of Reason).

entailment
the intuitive notion of strict logical implication, such that necessarily if p, then q (that is, it is impossible that p and not q).

essence
for Aristotle, that which remains the nature of a thing throughout its change from potentiality to actuality. More generally, the necessary defining characteristic of a thing, such that without that characteristic the thing would not be the thing it is. ethical intuition the immediate awareness of an ethical property or an ethical truth, but for Rawls intuitionism is the claim that there is an irreducible body of first principles which cannot be ordered in terms of priority.

ethical intuition
the immediate awareness of an ethical property or an ethical truth, but for Rawls intuitionism is the claim that there is an irreducible body of first principles which cannot be ordered in terms of priority

ethical naturalism
the view, criticized by G. E. Moore, that ethical properties like goodness can be defined in terms of the natural properties that justify their use. Moore's alternative account in terms of non-natural intuition of goodness has seemed implausible, but new ways of conceiving relations among properties have also been important in the revival of ethical naturalism.

eudaimonia
flourishing or well-being, the central aim of Aristotelian ethics, the realization of which is a complete and self-sufficient combination of virtue and its rewards in happiness. It is important to realize the complexity of the notion and not to reduce it to one of its components.

event
we can think of events as changes in objects or in relations among objects, so that the basic entities in our account of the world are objects and relations rather than events. However, some philosophers see advantages in recognizing events as basic, although events might have to take on some of the character of objects for this to be acceptable.

evolutionary epistemology
an approach to the development of human knowledge in evolutionary terms, either as an integral part of natural selection or as an independent process modelled on biological natural selection. Evolutionary epistemology is part of a broader programme of naturalized epistemology. Rather than seeking to secure our knowledge claims against sceptical doubts, naturalized epistemology tries to explain major features of our knowledge as necessary or inevitable features of ourselves as natural beings.

expert system
computer with 'built-in' expertise, which, used by a non-expert in a particular subject area, can evaluate or make other decisions concerning that subject.

explanation
an account characteristically telling us why something exists or happens, or must exist or happen. The covering law model of explanation proposed by Hempel has been widely influential, but has many critics. There are controversies over the nature of functional or teleological explanation, over the legitimacy of inferring to the best explanation, and over Dilthey's contrast between scientific explanation and historical understanding.

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fallibilism
Peirce's view that none of our beliefs, even the apparently most fundamental, is certain and that any of our beliefs can be revised. Peirce believed that, rightly understood, relinquishing certainty does not open the way to sceptical doubt

family resemblance
Wittgenstein's term in his later philosophy for the way in which expressions apply to things or kinds of things not sharing a common defining property, but instead sharing some of an interwoven complex of likenesses, as in the facial features of family members. He made the same point regarding the overlapping features of games.

fictional entities
not all expressions pick out things which exist. Non-existing or fictional entities can play havoc with our account of language and reality. If they do not exist, we are tempted to enrich our ontology with an existence-like status to allow reference to them. Analysis, in one form or another, might avoid such temptations by showing that we can mean what we need to mean without committing ourselves to odd ontological items. Problems remain for real as opposed to notional fictions. We can say what is true or false about Anna Karenina or Sherlock Holmes, yet we cannot be certain how to understand our ability to do so.

first philosophy
in Aristotle, the study of the general characteristics of all types of existence or the principles of being. More generally, especially since Descartes, the position that there is an essential role for philosophy, prior to any science. Such a claim is challenged by scientistic views, which reverse the priority.

form of life
what Wittgenstein takes to be fundamental in his later account of understanding language as variously embedded in shared human activity. The crucial notion of 'form' shifts from logical form in his early writing to form of life. What is fundamental in understanding the possibility of language shifts from objects to language games and forms of life.

formal
in general, formal considerations have to do with the abstract structure, or pattern, of a subject, rather than with its content. Hence formal logic, for example, is concerned not with the content of particular sentences in an argument, but only with their structure of truth values.

foundationalism
the view that knowledge is possible only if some items serve as a certain foundation for the rest. Special attention is drawn to the alleged certainty of the proposed foundations and to the relation between the foundations and the rest of knowledge.

free will and determinism
there are threats to freedom involving the apparent determination of human action independent of our will. These include divine foreknowledge and in modern philosophy the possibility that our actions are determined by causal laws. One way out would be to argue that freedom and a particular form of determinism are compatible by showing that determinism has weaker implications than at first seems the case. One could also argue that what one values in freedom is not risked by determinism and is not aided by indeterminism. Nevertheless, some philosophers still claim that, on a proper understanding of freedom and foreknowledge or freedom and causal laws, we cannot have both.

function
a function is a relation between the value of variables and the value of the function as a whole. Giving a definite value to the variables yields a definite value to the whole function.

functional explanation
also teleological explanation, in which an item is explained by the role or function it has in producing something which promotes or preserves the entity or kind of entity of which it is a part. Functional explanation is prominent in biology and in some of the social sciences. There is disagreement whether functional explanation is a rival to causal explanation or a form of causal explanation.

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good
many approaches to ethics are centred on achieving what is good, although others are based on doing what is right. Priority to one goal need not exclude the other, but might shape the contents or limit how we pursue the other. We can ask about the relationship between human goodness and the goodness of other things, such as a knife that cuts well. On some views, goodness is reduced to one quality, like happiness or pleasure or satisfying desire, but others think of goodness as inherently complex. In either case, goodness has a place in moral psychology, motivating our actions and explaining our emotions.

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happiness
according to different ethical views, happiness might be one goal in life, the only possible goal, or a fortunate by-product of the pursuit of other goals. Happiness might concern one's aggregate of pleasure or require a complex balance involving virtue, pleasure, achievement and good fortune.

hedonism
the belief that pleasure is the greatest good and highest aspiration of mankind. In early utilitarian thinking, this belief provided the interpretation of 'utility' or 'good'.

hermeutics
a method of interpretation, initially of biblical texts but later extended to other texts and with Dilthey to whole cultures. Characteristically, the method improves our understanding of what is obscure, corrupt, or incomplete by placing it in the context of a whole. The hermeneutic circle is a problem which classically arises because the understanding of an item in a text depends on our understanding of the whole text, while the understanding of the whole text depends on our understanding of that and other items. This interdependence of interpretation, however, need not be vicious, although it might call for modesty rather than dogmatism in advancing any interpretation.

historicism
the view that concepts, beliefs, truths and even standards of truth can be understood only in relation to the whole moral, intellectual, religious and aesthetic cultures of the historical periods in which they arise or flourish. This position is linked to demands for a hermeneutic method to achieve appropriate understanding. The term is also used by Popper for the view that history is governed by necessary laws of development.

holism
the view that wholes have some priority over the elements, members, individuals or parts composing them. Social holism claims that individuals can be understood only in terms of the practices or institutions in which they take part and is a rival to some aspects of individualism. Methodological holism and methodological individualism propose different methodological constraints on the study of phenomena without pronouncing on their real constitution, while metaphysical holism claims that wholes are distinct entities, whose existence cannot be reduced to that of the items composing them. Holistic views in the philosophy of science and the philosophy of language propose that the meaning and truth of our claims cannot be assessed one by one, but must be assessed as part of theories, bodies of theory, or all we believe about the world.

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iconographic
derived from the Greek word for 'image': hence, an artefact of some kind (such as a painting) that visually resembles the object it represents.

idealism
the view that the existence of objects depends wholly or in part on the minds of those perceiving them or that reality is composed of minds and their states. There are many varieties of idealism, ranging from Plato's doctrine of independently existing ideas or forms to Berkeley's subjective idealism and Hegel's absolute idealism. Kant attempted to combine empirical realism with transcendental idealism.

ideas
for Plato, the unchanging independently existing bases of the perceived world and thought about the world, and in seventeenth- and eighteenth-century philosophy, the vehicles of sensory representation of external objects and of thought. Locke and Leibniz initiated disputes whether ideas could be innate, in us independent of sensory experience. Berkeley rejected Locke's distinction between the ideas of primary qualities (which resemble the qualities that produce them) and the ideas of secondary qualities (which are produced by qualities that they do not resemble). Hume argued that ideas originated in impressions, but still retained sensory and intellectual functions for ideas. Kant separated these functions (and used the term 'idea' for other purposes).

identity
in order to use a concept we must be able to individuate different entities falling under that concept and to identify these individual entities over time. It is unclear whether or not individuating and identifying entities must refer to the kind concepts under which they fall. A special case of identity, discussed by Locke, Hume and many contemporary philosophers, is personal identity. Both the memory and bodily criteria for personal identity have encountered difficulties, leading Parfit to question the importance of personal identity. The identity theory of mind, according to which mental states are identical with states of the central nervous system led to much discussion, although other forms of materialism have supplanted it in current controversy. Kripke's rejection of the notion of contingent identity in favour of necessary identity helped to renew discussion of the nature of the identity relation itself.

illocutionary act
in J. L. Austin's theory of speech acts, what one does in uttering what one utters. A perlocutionary act is what one does by uttering what one utters.

immaterial substance
Berkeley argued that the notion of material substance could not be sustained, but that immaterial substances, human minds and God, were crucial to our account of reality.

immutable
literally, not able to change.

individualism
an approach to ethics, social science and political and social philosophy which emphasizes the importance of human individuals in contrast to the social wholes, such as families, classes or societies, to which they belong. In different contexts, individualism is contrasted to holism and collectivism. Metaphysical individualism claims that social objects like societies can be reduced to individuals. Methodological individualism does not make metaphysical claims, but rather constrains the ways we explain social action.

induction
a process of reasoning contrasted with deduction in which conclusions are drawn that all individuals of a kind have a certain character on the basis that some individuals of the kind have that character.

inference
the process of reasoning whereby one statement (the conclusion) is derived from one or more other statements (the premises).

infinite regress
an infinite regress in a series of propositions arises if the truth of proposition P1 requires the support of proposition P2, and for any proposition in the series Pn, the truth of Pn requires the support of the truth of Pn+1. There would never be adequate support for P1, because the infinite series needed to provide such support could not be completed.

intensionality
a feature characterizing sentences about mental states, according to which the truth value of the sentence may be altered by replacing expressions in the sentence by other expressions referring to the same objects. In extensional contexts, unlike intensional contexts, such substitutions do not affect the truth value of the sentence.

intentionality
a characteristic feature of mental and linguistic states according to which they have an object or content and are thus about something.

irreducible
to reduce Xs to Ys would be to show how Xs were, in reality, only Ys or in a linguistic guise to show that X-talk could be systematically eliminated in favour of Y-talk in a way involving no loss of content. Properties are said to be irreducible then, if they resist such reductions.

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Leibniz's Law
if A=B, for any true statement about A there will be a corresponding true statement about B, and vice versa. There are disputes over the way to deal with statements for which this law does not seem to hold.

logical atomism
the view held for a time by Russell and Wittgenstein that for language to have meaning it must be analysable into mutually independent propositions, the atomic elements of which correspond to elements in states of affairs. For Wittgenstein at this stage, propositions had meaning by logically picturing possible states of affairs. Russell's logical atomism, unlike Wittgenstein's, was tied to an empirical interpretation.

logical positivism
a general philosophical position, also called logical empiricism, developed by members of the Vienna Circle on the basis of traditional empirical thought and the development of modern logic. Logical positivism confined knowledge to science and used verificationism to reject metaphysics not as false but as meaningless. The importance of science led leading logical positivists to study scientific method and to explore the logic of confirmation theory.

logomachy
a controversy of no real substance, depending on a merely verbal dispute.

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material biconditional
a controversy of no real substance, depending on a merely verbal dispute. material biconditional the biconditional if and only if ('iff') is a relation between two statements p and q, such that p implies q and q implies p. The biconditional is material if the implications are contingent and strict if the implications are necessary.

materialism
the doctrine that all items in the world are composed of matter. Because not all physical entities are material, the related doctrine of physicalism, claiming that all items in the world are physical entities, has tended to replace materialism.

maxim
a statement expressing a general truth or rule of conduct.

method
philosophical methods are combinations of rules, procedures and examples determining the scope and limits of philosophy and establishing acceptable ways of working within those limits. The question of philosophical method is itself a matter for philosophy and constitutes a major feature of philosophy's reflective nature. Philosophers disagree about what is an appropriate philosophical method and about the relationship between philosophical method and the methods of other disciplines, especially scientific method.

methodological
concerning the study of method, particularly scientific method. Questions asked in contemporary methodology concern not only the characterization of scientific method, but also whether a single such characterization is necessary, or can do justice to the multitude of approaches and devices actually used.

model
in science, a representation such that knowledge concerning the model offers insight about the entity modelled. Whether models are heuristic devices or essential features of scientific explanation is a matter of debate. Mathematical models are interpretations of a formal system assigning truth values to the formulae of the system, thus testing the system for con-sistency.

modern
for philosophical purposes, the period of philosophy and general intellectual life following Descartes and his contemporaries. The broad characteristics of the period are often taken to include an emphasis on individualism, the intellect, the universality of judgement, and the consequence of adopting these features as starting points.

modus ponens and modus tollens
modus ponens, or affirming the antecedent (the if clause in an if-then proposition), is an argument of the valid form, 'If p, then q; p; therefore q'. Modus tollens, or denying the consequent (the then clause in an if-then proposition), is an argument of the valid form, 'If p, then q; not q; therefore not p.'

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natural selection
central thesis of the biologist Charles Darwin which suggests that within every population of living organisms there are random variations which have different survival value. Those which aid survival (or enhance reproductive capacity) are 'selected' by being genetically transmitted to succeeding generations.

neutral monism
a position according to which the difference between minds and bodies derives from different arrangements of the same neutral entities. The entities are neutral because they themselves are neither mental nor physical. This position proposed a solution to the mind-body problem, but there are difficulties with the neutral status of that which constitutes minds and bodies and with how arrangements of what is neutral can issue in minds and bodies. If experiences are proposed as the neutral entities, it is not clear whether neutral monism clarifies or obscures the nature of experience.

nominalism
the view that the only feature that particulars falling under the same general term have in common is that they are covered by the same term. Nominalism is opposed to realism, for which universals are required to explain how general terms apply to different particulars. For nominalism, language, rather than independent reality, underlies perceived likeness. Many philosophers are attracted to the ontological austerity of nominalism, but problems remain concerning how language, especially predication, works on nominalist principles.

non-Euclidean geometry
Euclids's Fifth 'Parallels' Postulate (or Axiom XI) is rendered informally as: 'through a given point P not on a line L, there is one and only one line in the plane of P and L that does not meet L'. Non-Euclidean geometries explore systems in which two different denials of this postulate are used: Lobachevskyan geometry contains an infinite number of parallels through P; Reimannian geometry contains no parallels through P. Reimannian geometry has played a crucial role in the development of the general theory of relativity.

non-monotonic logics
in logic, deductive validity is cumulative, or monotonic, in that no matter what further premises are added to an originally valid argument, the argument remains valid. Non-monotonic logics, used in artificial-intelligence research, explore logical systems in which monotonicity does not hold.

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Ockham's Razor
the principle enunciated by the medieval nominalist William of Ockham that entities are not to be multiplied beyond necessity. Applied to systems of ontology or bodies of scientific theory, the principle encourages us to ask whether any proposed kind of entity is necessary. This principle of metaphysical economy retains influence in contemporary philosophy, although in judging rival systems it is not always clear which best meets the requirements of Ockham's Razor.

omnipotence and onmiscience
attributes of being all powerful and all knowing, traditionally ascribed to God. The two combined with divine goodness give rise to the problems of explaining how there can be evil in the world. Puzzles about omnipotence have led to explanations that it is constrained by logical and metaphysical possibility. Divine omniscience, including foreknowledge, has been seen as a threat to human free will, and other philosophers have been concerned about what an omniscient being without a body in space and time could know.

ontology
the study of the broadest range of categories of existence, which also asks questions about the existence of particular kinds of objects, such as numbers or moral facts.

operator
an expression which alters the logical properties of other expressions to which it is applied. A sentential operator can be applied to sentences to yield new sentences.

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paradox
an argument which seems to justify a self-contradictory conclusion by using valid deductions from acceptable premises.

perception
our awareness of the world and its contents through sensory experience. The analysis of perception and the attempt to deal with skeptical arguments about perceptual knowledge are central philosophical topics. Perception involves both our capacity to be sensorily affected by external objects and our ability to bring these objects under concepts, although other capacities might also have a role to play. What we perceive and how these objects of perception are related to us and to physical objects are matters of continuing concern.

phenomenology
for Hegel, the study of the dialectical development of Spirit through stages towards rational, self-conscious freedom; for Husserl, a philosophical method based on the reflective and descriptive study of consciousness focused on the intentionality of mental states. The structure of consciousness revealed, which includes an ego that exists absolutely, aimed to provide a sure foundation for knowledge. In response to Frege's early criticism, Husserl attempted to draw a sharp boundary between phenomenology and psychology. In his later writing, Husserl altered many features of his notion of phenomenology, and other writers, especially Heidegger, used the term in radically different ways.

picture theory of meaning
Wittgenstein's view in the Tractatus Logico-Philosophicus that a proposition has meaning in virtue of sharing a form with an actual or possible state of affairs. The proposition provides a logical picture of the state of affairs, and is true if its elements stand in the same relation as the objects in the state of affairs. Philosophers disagree over the extent to which Wittgenstein moved away from this theory in his later writings.

pluralism
in metaphysics, the belief that there is more than one kind of fundamental reality or of fundamental existents. Hence, pluralism stands in contrast to monism (one kind of fundamental reality or existent) and dualism (two kinds of fundamental reality or existent). In ethics, the belief that there is more than one kind of fundamental good or supreme ethical value.

possible world
the analysis of statements in terms of 'possible worlds' comes from the semantic treatment of modal logic - the logic of possibility and necessity. A possible world is a way the world might have been. A necessary statement is one that is true in all possible worlds; a contingent statement is one that is true in at least one possible world.

postmodernism
if Descartes is seen as the father of modernism, then postmodernism is a variety of cultural positions which reject major features of Cartesian (or allegedly Cartesian) modern thought. Hence, views which, for example, stress the priority of the social to the individual; which reject the universalizing tendencies of philosophy; which prize irony over knowledge; and which give the irrational equal footing with the rational in our decision procedures all fall under the postmodern umbrella.

prescriptive statement
a statement, for example in ethics, which says how things should be, as opposed to a descriptive statement, which says how things are.

presupposition
a generally implicit assumption (though it can be made explicit) underlying a claim or a process of inference.

primary and secondary qualities
seventeenth-century scientists and philosophers attempted to distinguish qualities like size and shape, which produce in us ideas (ideas of primary qualities) that resemble the qualities themselves, from qualities that produce in us ideas (ideas of secondary qualities), like colour and taste, which do not resemble the qualities themselves. The former ideas, unlike the latter, offered something that could be measured, and were thus considered a suitable basis for scientific explanation. Berkeley argued against the distinction.

principle of non-contradiction
the logical principle rejecting the possibility that propositions of the form 'p and not p' are true, that a subject can be and not be, or that we can ascribe and deny the same attribute to the same subject.

proposition
that which is characteristically stated by a declarative sentence and can be true or false. Understanding the nature and structure of propositions is often seen as the central task of the philosophical examination of logic. Philosophers consider the apparently different functions of components of propositions (names, predicates and logical constants) and how they are unified into something capable of having a truth value. They ask about how the form, meaning and use of propositions are related and how different propositions have logical relations. They ask how linguistic or psychological states can have propositional contents. The existence of propositions, as opposed to sentences, is challenged by those suspicious of their abstract nature.

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quantifier
modern predicate logic uses quantifier expressions some ($) and all (") in sentences with variables (x, y, . . . ), predicates (F, G, . . . ), relations (R, . . . ), identity and logical constants (and, or, not, if-then). ($x) ($y) (if Fx and Gy, then x=y) reads 'For some x and for some y, if x is F and y is G, then x is identical with y'. The individual or multiple use of the universal quantifier 'all' and the existential quantifier 'there exists' to bind variables in sentences has been seen as the key to the development of a powerful and flexible system of modern predicate logic.

quantum mechanics
a modern physical theory (much developed and refined since Neils Bohr's ground-breaking work in 1913) which deals with the structure and behaviour of subatomic particles. It has given rise to philosophical problems of its own (some quantum phenomena seem to require a non-classical logic) and has also been used by both sides in the philosophical dispute between realist and instrumentalist construals of scientific theories.

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rational numbers
any number of the form x/y, where x can be any positive or negative integer or 0, and y is a positive integer. An irrational number is any real number which is not rational.

real number
a real number is any number which can be represented as a non-terminating decimal.

realism
a variety of doctrines in different areas of philosophy holding that entities or facts of contested sorts exist. There are, of course, different arguments concerning the reality of numbers in mathematics, the reality of moral facts in ethics, and the reality of time in physics or metaphysics. The kind of reality ascribed to universals differs from the kind of reality seen as belonging to common-sense material objects or to theoretical entities in science. Various realisms are hence opposed by nominalism, idealism, instrumentalism, reductionism, eliminativism, conventionalism, constructivism, relativism and anti-realism. Kant argued for both empirical realism and transcendental idealism. In recent years, many philosophers have discussed Michael Dummett's argument for anti-realism, in which he rejects the claim that every proposition must be either true or false and argues that realism must be false because it implies this claim.

reason
an ability to move from the truth of some beliefs to the truth of others. Some philosophers have seen this capacity as more or less sufficient to determine one correct systematic account of reality, while others have argued that such an account, if possible at all, must be based primarily upon experience. Kant, following Aristotle, saw reason divided between theoretical and practical reason, the latter issuing in actions rather than beliefs, but held that at a deep level the two capacities were the same. Hegel saw reason and much else altering at different stages of historical development. Hume restricted practical reason to finding means to obtain ends set out by the passions, others have rejected the means-ends account. Reason enters the account of institutions through models of the interaction of the choices of individuals and through the direct assessment of practices and societies.

recursive function
a function for which the value of the function for any argument Xn+1 is a function of the value of the function for the argument Xn.

reflective equilibrium
a term used by Nelson Goodman and John Rawls for a two-way reconciliation between judgements and principles. Judgements about individual cases are guided by principles, but principles can be modified in light of judgements. Equilibrium is reached when principles and judgements fit one another without further alteration. An equilibrium is always liable to be upset by new cases, but that is also true, although less transparently so, if one tries to determine principles by other procedures.

relativity (theory of )
the special theory of relativity is a modern physical theory due to Einstein, giving an account in which neither space nor time has an independent absolute value or existence but is each relative to the other. Thus the classical view of space and time is replaced with one in which the two are aspects of the same underlying reality: Space-time. The general theory of relativity extended the special (from considering frameworks in uniform relative motion to considering frameworks in arbitrary relative motion to one another) and is the currently accepted basis for our theory of gravitation.

rights
legal or moral capacities, often correlated with duties, which may be exercised without interference by others, including the state, or in some cases with the assistance of others. Rights can regard such matters as belief, actions, relationships, property, or the safety and integrity of oneself. Some rights involve limiting the rights of others or the creation of duties. Rights can be considered one by one or from the standpoint of a system of rights and duties. Philosophers discuss the status of rights in morality, in particular whether rights can provide the basis of moral or political philosophy or must be understood within the context of other notions, such as principles, virtues, utility, or a social contract, from which their legitimacy might derive. Philosophers have discussed the claim that rights 'trump' other considerations, the claim that there are collective as well as individual rights, and the claim that animals have rights. Exploring this last question can help to see what one must be like in order to hold rights. Philosophers have also considered the relationship between legal and moral rights and, in the face of Bentham's attack on natural rights, have examined the notion of natural, universal or human rights.

rigid designator
a subject term designating the same object in all different possible situations (or possible worlds) in which the object exists, so long as the meaning of the term is held constant. A non-rigid designator with constant meaning can designate different objects in different possible situations (or possible worlds).

rule
a principle guiding action. For Kant, concepts are rules, the understanding is the faculty of rules, and our use of rules is central to our account of objectivity. Much of Wittgenstein's discussion of following a rule runs parallel to the Kantian insight that rules do not determine their own application. The question of what gives a rule authority and holds it and its application in place led to the rejection of the possibility of a private language and Wittgenstein's emphasis on practices and forms of life. Interrelations among rules, roles and practices are central concerns in the philosophy of social science. Discussions of what constitutes a legal rule and how such rules have normative force are main features of the philosophy of law.

rule utilitarianism
a version of utilitarianism in which general rules rather than acts are assessed for utility, thus shifting concern from individuals to practices and institutions. Acts are endorsed not in their own right, but because they accord with practices or institutions which meet the test of maximizing utility.

Russell's Paradox
a paradox based on the notion of class membership discovered by Bertrand Russell and undermining the crucial notion of class or set in Frege's foundations of mathematics. The paradox led to important changes in set theory and in the notion of a set, in part also to prevent further paradoxes from arising. The paradox arises from asking whether the class of all classes that are not members of themselves is a member of itself.

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sanctions
negative and positive sanctions are punishments or rewards for behaviour that transgresses or is in accord with a rule.

scope
in logic, the shortest propostional fucntion in which a logical operator occurs. Scope ambiguities are common in ordinary language but are eliminable during formalization.

semantics
in the study of language, semantics is concerned with the meaning of words, expressions and sentences, often in relation to reference and truth. Semantics is contrasted with syntax (the study of logical or grammatical form) and pragmatics (the study of the contribution of contextual factors to the meaning of what language users say). Meta-semantic theories study key semantic notions such as meaning and truth and how these notions are related.

sense data in empiricist theories of perception, which were popular earlier this century, that which is given by the senses. Questions arise concerning whether anything is purely given in perception, what might be given, and how what is given might be related to the external objects of common sense.

set
a set is a collection of definite distinguishable entities. Set theory, however, allows for the null set: the set that has not members.

social contract
an actual or hypothetical contract providing the legitimate basis of sovereignty and civil society and of the rights and duties constituting the role of citizen. The contract can be agreed between people and a proposed sovereign or among the people themselves.

solipsism
the view confining reality to oneself and one's experiences.

subjective-objective distinction
distinction the subject contributes what is subjective to such things as perceptual, moral and aesthetic judgement and experience; the objects of such judgements and experience contribute what is objective. The subjective seems prone to variation among subjects, while the objective appears to provide a basis for universal agreement. There is disagreement over the contribution of the subject and the object to such judgements. Different notions of objectivity might be suitable in different domains. Historical judgements, for example, might be objective if the historian making them is unbiased rather than through having a favoured relation to relevant objects.

sublation
a change which both cancels and preserves an entity or concept by raising it to a higher level. The full complex meaning of this term (aufheben in German) was established by Hegel.

substance
something which can exist by itself, is the substrate underlying the existence of other things, and is the subject of which other things are predicated. In his Metaphysics Aristotle considered what can be substance: matter, form, or a combination of matter and form. According to various criteria he used, different answers seemed plausible, although he finally preferred form. Seventeenth-century philosophers, including Descartes, Spinoza and Leibniz, came to strikingly different solutions to the problem of what qualifies as being substance. Locke's account seems to suggest an unknowable substratum which falls out of any account of knowledge, but it can also be seen to offer a corpuscular substrate linked to his doctrine of primary qualities and their explanatory role in science.

sui generis
literally, of its own kind, or unique.

supervenience
a property F supervenes on a property G, firstly, if anything which has property F has it in virtue of having property G and, secondly, if something has property F in virtue of having property G, then anything else having property G would also have to possess property F. Supervenienceis intended to allow for non-reductive relations among hierarchies of properties.

syllogism
an argument according to Aristotle's logical theory involving a major premise, a minor premise, and a conclusion.

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things-in-themselves
things-in-themselves Kant distinguished appearances (phenomena) from things-in-themselves (noumena). Things-in-themselves are meant to exist independently of how we experience them, in particular independently of space, time and the categories.

thought
for Frege, a thought is the sense of a sentence which can be used to make an assertion or to ask a question that is answerable by either 'Yes' or 'No'. The contents of thoughts can be true or false. Thoughts in this sense are logical or conceptual rather than a matter of individual psychology. Different individuals may share the same thought, although they cannot share the same act of thinking.

thought experiment
an attempt to conceive the consequences of an intervention in the world without actually intervening. In some cases, an actual experiment would be preferable but is impossible in practice or perhaps even in theory.

three-valued logic
classical logic allows 'true' and 'false' as the only values for propositions, as expressed by the law of excluded middle (which states that every proposition is either true or false). Three-valued logic can reject this law by adding an additional value like 'indeterminate' or can replace the two initial values with three other values like Ônecessarily trueÕ, 'necessarily false', and 'contingent'.

transcendental
for Kant, 'transcendental' is contrasted with 'transcendent'. Something transcendent goes beyond the limits of experience, while something transcendental relates to the conditions of the possibility of experience.

truth
propositions, statements, sentences, assertions and beliefs have been offered as appropriate bearers of truth or falsity. Understanding truth is filled with difficulty. Philosophers have explored the possibility that truth is: a correspondence between what we say and how things are; a matter of coherence between statements and a background of settled beliefs; an ideal limit which enquiry will approach; a feature of assertions which function well in enquiry or in life more generally; a matter of giving a truth definition for a language; a redundancy, because 'It is true that p' is equivalent to 'p'; or disclosedness of being. Some of these theories are compatible and might be integrated in a more comprehensive theory. On some accounts, each proposition is true or false on its own, while others adopt a holistic view. The relation between meaning and truth is of central philosophical concern.

truth function
the truth value of a combination of propositions which depends only on the truth values of the constituent propositions and the logical constants (and, if-then, or, not) by which they are combined. Truth functions can be set out in truth tables:

 p qp or q

 

 T T    T

 T F    T

 F T    T

 F F    F

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understanding
the capacity to use concepts and to bring individuals under them. Kant distinguished sensibility, understanding and reason as fundamental to our capacity for experience and knowledge. He understood concepts as rules and saw the understanding as the faculty of rules, including both empirical concepts and the categories as pure concepts of the understanding. In the social sciences and history, Dilthey and Weber have contrasted understanding (verstehen) and explanation, with explanation providing the causal accounts of science and understanding offering insight into such things as human lives, culture and historical periods. Hermeneutics has been proposed as the method appropriate to understanding. Philosophers have disagreed over the claimed difference between explanation and understanding, about the character of understanding, and about the methodolog-ical implications of recognizing understanding as a distinctive mode of knowledge.

universals
abstract objects intended to explain how general terms have meaning and how they apply to individuals. There were medieval disputes over universals involving realism, which accepted their existence, and nominalism, which denied it. Some philosophers see problems in embracing any abstract object, especially in this case because their relation to individuals seems opaque, yet it is also difficult to see how an account of how names have meaning and refer to individuals will explain the contribution of predicates and relations to the meaning and truth or falsity of sentences or propositions. Explaining these roles might not require classic universals, derived from independently existing Platonic forms, but there are other possibilities short of nominalism.

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verification principle
a central doctrine of logical positivism according to which the meaning of a proposition is its method of verification. Claims without a method of verification, such as those of religion and metaphysics, are meaningless. Verificationism thus offered a criterion of meaningfulness.

verisimilitude
literally and as used in aesthetic criticism, the appearance of being true or real. In philosophy, a surrogate for the truth of scientific theories offered by Karl Popper as part of his vision of the nature of scientific progress.

vicious regress
an attempt to solve a problem which re-introduced the same problem in the proposed solution. If one continues along the same lines, the initial problem will recur infinitely and will never be solved. Not all regresses, however, are vicious.

Vienna Circle
an intellectual (mostly philosophical) group, led by Moritz Schlick, which met from 1924-36, though its influence continued for much longer. Their general position, pro-science and hostile to speculative metaphysics, gave rise to the doctrines of logical positivism.

virtue
an excellence of moral or intellectual character. Plato, Aristotle and many subsequent philosophers explored the nature of the virtues, their relations among themselves and to non-virtuous states, their place in our psychology and their role in achieving happiness. Virtues offer a basis for ethical life rivalling those provided by Kantian principles or a utilitarian calculation of happiness, although an account of ethics might reasonably include principles, consequences and virtues. A recent revival of virtue ethics has been motivated in part by dissatisfaction with the abstract universal nature of the main alternative views. The emphasis on cultivating virtues in concrete human individuals could correct this, but it is not clear that a perfectionist concern for individual excellence is satisfactory to ground ethics.

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*Courtesy of The Blackwell Companion to Philosophy A-Z