ELI5: Explain Like I'm 5

Foundationalism

Foundationalism is a way of thinking about knowledge that says that all knowledge is built on a “foundation” of ideas that are certain and cannot be doubted. This foundation is usually made up of basic facts like “the sun rises in the morning” that everyone can agree on. From this foundation we can build more complex ideas, like math equations or scientific theories, that rely on the “foundation” being true.