Montaigne’s more theoretical arguments went to the heart of theories of knowledge. All human knowledge comes from sense experience, but all humans perceive things differently and we are all vulnerable to illusions, dreams, and ordinary distortions of perception. On top of these doubts, Montaigne then introduced “the problem of the criterion.” We need a criterion to determine if our experience is reliable as a basis for knowledge, but the criterion itself needs to be tested and for that a second criterion is necessary, and to test this second criterion, a third one is necessary, and on and on. All theoretical and natural philosophers after Montaigne had to come up with some sort of answer to the skeptical problems he raised: the unreliability of sensory information; the disagreement of experts; cultural differences in values and customs; individual differences in perception; the possibility of human error; and above all, the necessity for a criterion, or neutral standard to settle disagreements.