According the Stanford Encyclopedia, much of epistemology has arisen in defence of, or in opposition to various forms of skepticism.
“For example, rationalists could be viewed as skeptical about the possibility of empirical knowledge while not being skeptical with regard to a priori knowledge and empiricists could be seen as skeptical about the possibility of a priori knowledge but not so with regard to empirical knowledge.”
Restricted forms of skepticism can refer to common philosophical problems such as the problem of other minds or the problem of induction. That is, we cannot have knowledge of any propositions in a particular domain. Skepticism in general, however, refers to questioning the validity of our knowledge in domains in which we commonly accept that we have knowledge. Therefore skepticism questions the notion of foundationalism.
From the Stanford Encyclopedia:
“Foundationalism is a view about the structure of justification or knowledge. The foundationalist’s thesis in short is that all knowledge and justified belief rest ultimately on a foundation of noninferential knowledge or justified belief.”
Epistemic Regress Problem:
Any proposition requires a justification (justified true belief). Any justification in turn requires support. Therefore the justifying of propositions is endless. “… why? why? why? but why? …”
Foundationalism seeks to address this issue by suggesting that there are some basic beliefs that do not need justification, upon which all knowledge is built. This means that some things must be true in and of themselves. (what might Heidegger make of this?)
A priori: independent of experience
A posteriori: dependent on experience or empirical evidence
Three Problems for Foundationalism:
1) Poverty of Foundations;
the foundations aren’t enough to build our knowledge upon. They are too limited. A foundationalist might reply with words to the effect that this is just the way it is, for better or worse.
Descartes used method of radical doubt to arrive at certainty. He was unable to doubt his own existence (cogito). Descartes sought to prove existence of external world on basis of clear and distinct ideas. The Cartesian circle is the result of using clear and distinct ideas to prove the existence of God, and then appeal to God to prove certainty of such ideas.
Ultimately it becomes hard to prove there is such a thing as an external world if we require certain foundations for knowledge.
2) Unjustified Foundations (version 1)
arbitariness of foundations
The foundations themselves don’t have justification. So a foundationalist might try to provide justification. However, by justifying a foundational belief, the foundation is no longer playing its role as it is now the result of a justification from elsewhere. So either: you don’t justify the foundational belief and they are just arbitrary, or you justify and they’re not playing their role any more.
3) Unjustified Foundations (version 2)
For sense experience to justify some kind of belief, the sense experience has to have some form of content. So the question is raised as to whether sense experience involves making a judgment that something is the case, or is it just something that happens to you. Is sense experience a cognitive state? If an experience is a cognitive state, then it is the kind of thing that can provide justification for a belief. But, if it is not a cognitive state, simply a sensation, that does not need to be justified or unjustified, it is not clear how it can actually justify a belief.