What is the Foundation Principle of Human Knowledge?
Is knowledge gained through the use of reason? Or does it perhaps stem from the experience of the senses?
Much of the history of Western philosophy has been influenced by the basic difference between reason and experience as the foundation principle of knowledge. Specifically, it is the main bone of contention between rationalism and empiricism, two extremely influential philosophical strands. To understand what is at issue between rationalist and empiricist theories of knowledge, it is useful to look at three key distinctions that are used by philosophers to differentiate between them.
A Priori vs. A Posteriori
Something is knowable a priori if it can be known without reference to experience, without any empirical investigation of how things actually stand in the world. By contrast, if such investigation is needed, something is only knowable a posteriori.
Analytic vs. Synthetic
A proposition is analytic if it does not give any more information than is already contained in the meanings of the terms involved. Effectively, an analytic proposition is one that is apparent merely by virtue of understanding the meaning and relation of the words used. By contrast, a statement is synthetic if it brings together different concepts and so provides significant information (or indeed misinformation).
Necessary vs. Contingent
A necessary truth is one that could not be otherwise, it must be true in any circumstances and in all worlds. A contingent truth is true but might not have been if things in the world had been different.
Rationalism and Empiricism
After considering these three distinctions it would seem that there is an alignment between them. It would seem that an analytical statement, if true, is necessarily so and is known a priori while a synthetic proposition, if true, is contingently so and is known a posteriori.
Of course in philosophy things are never that straightforward and the main difference between empiricists and rationalists can be identified from the different way they choose to line up these terms. Rationalists seek to show that there are synthetic a priori statements, that meaningful facts about the world can be discovered by rational, non-empirical means. Empiricists, on the other hand, aim to show that apparently a priori facts (such as those found in the study of mathematics) are in fact analytical.
Alternatives to Foundationalism
While rationalists and empiricists differ on many things, they do agree that there is some basis (whether it be reason or experience) on which human knowledge is founded. Effectively, both rationalism and empiricism are essentially foundationalist. There are of course other approaches that dispense with this basic assumption of foundation. One influential approach is coherentism, in which knowledge is seen as in interlocking mesh of beliefs, all the strands of which support each other to form a coherent body or structure, but it is a structure without a single foundation.