Foundationalism is the general name for theories in epistemology (typically, theories of epistemic justification, but also of knowledge or other types of positive epistemic status) that hold that beliefs are justified (known, etc.) based on what are called basic beliefs (also commonly called foundational beliefs). 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 be self-justifying, that is, they are justified but not justified by other beliefs. Typically and historically, foundationalists have held that basic beliefs are justified by mental events or states, such as experiences, that do not constitute beliefs (these are called nondoxastic mental states).
Hence, generally, a foundationalist might offer the following theory of justification:
- A belief is epistemically justified iff (1) it is a basic/foundational belief (i.e., it is justified by a nonbelief), or (2) it is justified by a basic belief or beliefs, or (3) it is justified by a chain of beliefs that is supported by a basic belief or beliefs, and on which all the others are ultimately based.
Arguments for foundationalism
Foundationalists generally tend to argue that there must be some set of epistemologically basic propositions or else the process of justification will always lead to an infinite regress, like a four-year old constantly asking "Why?" See the regress argument in epistemology.
Historical foundationalism: rationalism vs. empiricism
Historically, two varieties of foundationalist theories were rationalism (or Rationalism, or Continental Rationalism, to refer to the historical movement) and empiricism (or Empiricism, or British Empiricism). Strictly speaking, neither empiricism nor rationalism is committed to foundationalism (it is possible to be an empiricist coherentist, for example, and that was a common epistemological position in 20th century philosophy).
Rationalism is the general name for epistemological theories that maintain that the reason is the source and criterion of knowledge. Rationalists generally hold that so-called truths of reason are the (most important) epistemologically basic propositions. Rene Descartes famously held that some of these truths are known innately and therefore constitute epistemologically basic innate knowledge.
Empiricism is the general name for epistemological theories that maintain that sensation reports are the source and criterion of knowledge. Classical empiricists generally held that such reports are indubitable and incorrigible and therefore worthy of serving as epistemologically basic propositions.
Alternatives to foundationalism
Alternatives to foundationalism include coherentism and reliabilism (though this has sometimes been construed as an unusual variant of foundationalism). Contextualism (or, in a stripped-down version, the blind posits theory) is the epistemological version of relativism; relativism is more often regarded as a theory of truth than as a theory of justification or knowledge.