A little reflection suggests that the majority of what we know have that status only because we know other propositions. For example, you know that your neighbour have cancer only if you know some other claims such as your doctor reports this and doctors are reliable. The support these beliefs provide for your belief that your neighbour have cancer illustrates that your first belief is epistemically dependent on these other two beliefs. This is a problem of relying yet on one belief to justify another belief and this other belief relying yet on another for justification and so on.
The response to this problem naturally raises the question about the proper epistemic structure for our beliefs. Should all beliefs be supported by other beliefs? Are some beliefs rightly believed apart from receiving support from other beliefs? All these is an attempt to halt the regress of justification and secure substructure that guarantees their certainty and justifies their truth. What is the proper structure of one’s knowledge or justified beliefs? The investigation on the foundation of knowledge focuses on the structural condition for justification. How should one’s belief be structured so as to be justified.
Any knowledge must either be foundational or depend for its justification, ultimately, on foundational beliefs. Suppose I claim to be justified in believing that my neighbour will die shortly and offer as my evidence that my neighbour has an untreatable and serious form of cancer. Concerned, you ask one how I discovered that my neighbour has cancer, and I respond that it is just a lunch on my part. As soon as you become convinced that I have no good reason to suppose that my neighbour has cancer, you will immediately conclude that my suspicion about my neighbour gives me no justification that he/she will soon die.
One might be able to convince oneself that one can know non-inferentially the principles of deductive reasoning, but deduction will not take one usefully beyond the foundation of knowledge and justified belief, there is a very real sense in which one doesn’t advance one’s knowledge significantly employing a form of reasoning that takes one only to conclusions that were implicitly contained in the conjunction of one’s premises.
On fallible knowledge, there is precious little included in the foundational justification of knowledge. How can one hope to get back the vast body of knowledge one pre-philosophically suppose one has, if one’s epistemic base is so impoverished?
We may question the incorrigible beliefs lying at the base of beliefs. For truth is always plural and situated. All thought are biased and there exist no position from which a correct view, in an absolute sense, may be grounded. Hence, one can conclude that we cannot have absolute certainty in the sense in which foundationalism defines certainty because, we cannot construct knowledge with absolute certainty starting from nothing.