In philosophy, Foundationalism is any theory in epistemology (typically, theories of justification, but also of knowledge) that holds that beliefs are justified (known, etc.) based on basic beliefs (also commonly called foundational beliefs). Alternative views are usually called anti-foundationalism. This position is intended to resolve the infinite regress problem in epistemology. Basic beliefs are beliefs that give justificatory support to other beliefs, and more derivative beliefs are based on those more basic beliefs. The basic beliefs are said to enjoy a non-inferential warrant (or justification). This warrant can arise from properties of the belief (such as its being self-evident or self-justifying).
Possible candidates for foundational beliefs are thought to include perceptual and memory beliefs, especially reports of one's own subjective experience; beliefs about the meanings of sentences or words; and a priori intuitions.
Foundationalism is an attempt to respond to the regress problem of justification in epistemology. According to this argument, every proposition requires justification to support it, but any justification also needs to be justified itself. If this goes on ad infinitum, it is not clear how anything in the chain could be justified. Foundationalism holds that there are 'basic beliefs' which serve as foundations to anchor the rest of our beliefs. Strong versions of the theory assert that an indirectly justified belief is completely justified by basic beliefs; more moderate theories hold that indirectly justified beliefs require basic beliefs to be justified, but can be further justified by other factors.
Classical foundationalism 
Foundationalism holds basic beliefs exist, which are justified without reference to other beliefs, and that nonbasic beliefs must ultimately be justified by basic beliefs. Classical foundationalism maintains that basic beliefs must be infallible if they are to justify nonbasic beliefs, and that only deductive reasoning can be used to transfer justification from one belief to another. Laurence BonJour has argued that the classical formulation of foundationalism requires basic beliefs to be infallible, incorrigible, indubitable, and certain if they are to be adequately justified. Mental states and immediate experience are often taken as good candidates for basic beliefs because it is argued that beliefs about these do not need further support to be justified.
Modest foundationalism 
As an alternative to the classic view, modest foundationalism does not require that basic perceptual beliefs are infallible, but holds that it is reasonable to assume that perceptual beliefs are justified unless evidence to the contrary exists. This is still foundationalism because it maintains that all non-basic beliefs must be ultimately justified by basic beliefs, but it does not require that basic beliefs are infallible and allows inductive reasoning as an acceptable form of inference. For example, a belief that 'I see red' could be defeated with psychological evidence showing my mind to be confused or inattentive. Modest foundationalism can also be used to avoid the problem of inference. Even if perceptual beliefs are infallible, it is not clear that they can infallibly ground empirical knowledge (even if my belief that the table looks red to me is infallible, the inference to the belief that the table actually is red might not be infallible). Modest foundationalism does not require this link between perception and reality to be so strong; our perception of a table being yellow is adequate justification to believe that this is the case, even if it is not infallible.
Reformed epistemology is a form of modest foundationalism which takes religious beliefs as basic because they are non-inferentially justified: their justification arises from religious experience, rather than prior beliefs. This takes a modest approach to foundationalism - religious beliefs are not taken to be infallible, but are assumed to be prima facie justified unless evidence arises to the contrary.
Internalism and externalism 
Foundationalism can take internalist and externalist forms. Internalism requires that a believer's justification for a belief must be accessible to them for it to be justified. Foundationalist internalists have held that basic beliefs are justified by mental events or state, such as experiences, that do not constitute beliefs. Alternatively, basic beliefs may be justified by some special property of the belief itself, such as its being self-evident or infallible. Externalism maintains that it is unnecessary for the means of justification of a belief to be accessible to the believer.
Reliabilism is an externalist foundationalist theory, initially proposed by Alvin Goldman, which argues that a belief is justified if it is reliably produced, meaning that it will be probably true. Goldman distinguished between two kinds of justification for beliefs: belief-dependent and belief-independent. A belief-dependent process uses prior beliefs to produce new beliefs; a belief-independent process does not, using other other stimuli instead. Beliefs produced this way are justified because the processes that causes them are reliable; this might be because we have evolved to reach good conclusions when presented with sense-data, meaning the conclusions we draw from our senses are usually true.
René Descartes 
Modern foundationalism was initiated by French Enlightenment philosopher René Descartes. In his Meditations, Descartes challenged the contemporary principles of philosophy by arguing that everything he knew he learnt from or through his senses. He used various arguments to challenge the reliability of the senses, citing previous errors and the possibilities that he was dreaming or being deceived by an Evil Demon. Descartes attempted to establish the secure foundations for knowledge to avoid scepticism. He contrasted the information provided by senses, which is unclear and uncertain, with the truths of geometry, which are clear and distinct. Geometrical truths are also certain and indubitable; Descartes thus attempted to find truths which were clear and distinct because they would be indubitably true and a suitable foundation for knowledge. His method was to question all of his beliefs until he reached something clear and distinct that was indubitably true. The result was his Cogito Ergo Sum - 'I think therefore I am', or the belief that he was thinking - as his indubitable belief suitable as a foundation for knowledge. This resolved Descartes' problem of the Evil Demon - the possibility that he was being deceived by an Evil Demon, rendering all of his beliefs about the external world false. Even if his beliefs about the external world were false, his beliefs about what he was experiencing were still indubitably true, even if those perceptions do no relate to anything in the world.
Critics of foundationalism often argue that for a belief to be justified it must be supported by other beliefs; in Donald Davidson's phrase, "only a belief can be a reason for another belief". For instance, Wilfrid Sellars argued that non-doxastic mental states cannot be reasons, and so noninferential warrant cannot be derived from them. Similarly, critics of externalist foundationalism argue that only mental states or properties the believer is aware of could make a belief justified.
According to skepticism, there are no beliefs that are so obviously certain that they require support from no other beliefs. Even if one does not accept this very strong claim, foundationalists have a problem with giving an uncontroversial or principled account of which beliefs are self-evident or indubitable.
Postmodernists and Post-Structuralists such as Richard Rorty and Jacques Derrida have attacked foundationalism on the grounds that the truth of a statement or discourse is only verifiable in accordance with other statements and discourses. Rorty in particular elaborates further on this, claiming that the individual, the community, the human body as a whole have a 'means by which they know the world' (this entails language, culture, semiotic systems, mathematics, science etc.). Thereof, the philosopher, in order to verify a particular means, or a particular statement belonging to a certain means (e.g. the propositions of the natural sciences) would have to 'step outside' the means they are judging and critique them neutrally, in order to provide a foundation for adopting them. However, this is quite literally impossible, the only way in which one can know the world is through the means by which they know the world, a method cannot justify itself. This argument can be seen as directly related to Wittgenstein's Theory of Language, drawing a parallel between Postmodernism and late Logical Positivism that is united in critique of foundationalism.
See also 
- Constructivist epistemology
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