The term foundationalism usually refers to theories about the structure of belief formation or belief justification. Beliefs may be formed or justified in one of two ways: non-inferentially (immediately) or inferentially (mediately). The division between "basic" and "nonbasic" beliefs is asymmetrical; nonbasic beliefs are formed or justified by appealing to basic beliefs, which are foundational. For classical foundationalists, a basic belief must be self-evident or incorrigible. Modest foundationalists argue that meeting other criteria, such as "evident to the senses," may also qualify a belief as basic; further, basic beliefs can be defeasible. Foundationalists in the science-religion dialogue often focus on defending the propriety of basic beliefs and inferences from them.

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