What is Intuition?
Intuition is a term employed widely and variously in everyday speech and in philosophy and science to mean "a way of knowing." Although its range of meanings is large, there is a common element in all its uses: intuition is a way of "knowing directly, excluding all inference, discursive reasoning, logic, and the employment of symbols and ideas (as in "a woman's intuition"). It also is a direct acquaintance with oneself that cannot be put into words, or a similar sensitivity to the thoughts and feelings of others.
The Philosophy of Intuition
Aristotle defined intuition as the mental acts by which the premises of all knowledge are revealed. In the Middle Ages the term was applied to the mystical or religious experiences of identification with God. Descartes spoke of rational intuition as the only means to certain knowledge and listed such propositions as "2 x 2 = 4" as those that are understood intuitively. Kant distinguished two forms of sensible intuition (space and time) that make knowledge possible.
Spinoza divided all apprehension into three kinds: sensory, rational, and intuitive. He held that intuition is of particular things, not of ideas. Although intuition customarily is viewed as a rational, or mental, act, Spinoza regarded it as a kind of behavior in which there is no distinction between the mind and the body.
In ethics, Kant and other philosophers thought that the apprehension of moral laws was by a special nonscientific faculty. George E. Moore and other ethical intuitionists developed the notion that certain actions have moral value that is apprehended immediately by moral intuitions.
In science, intuition is considered a way of arriving at truths that are felt to be valid in advance of proof (having a "hunch" or an insight). Scientists also employ the term for all intellectual mechanisms that are not clearly understood but that are characterized by rapidity.
In mathematics, intuitionism holds that the propositions of mathematics are constructs of the mind and do not refer to a Platonic realm of essences. The intuitionists are contrasted with the formalists and with those who believe that mathematical truths are deducible from immutable laws of logic.