EMPIRICISM, in philosophy, the theory that all knowledge is derived from sense experience (from Gr. 'Eµirapos skilled in, from irEipa, experiment). It is opposed to all forms of intuition alism, and holds that the mind is originally an absolute blank (tabula rasa), on which, as it were, sense-given impressions are mechanically recorded, without any action on the part of the mind. The process by which the mind is thus stored consists of an infinity of individual impressions. The frequent or invariable recurrence of similar series of events gives birth in the mind to what are wrongly called "laws" ; in fact, these "laws" are merely statements of experience gathered together by association, and have no other kind of validity. In other words from the empirical standpoint the statement of such a "law" does not contain the word "must" ; it merely asserts that such and such series have been invariably observed. In this theory there can strictly be no "causation" ; one thing is observed to succeed another, but ob servations cannot assert that it is "caused" by that thing ; it is post hoc, but not propter hoc. The idea of necessary connection is a purely mental idea, an a priori conception, in which observa tion of empirical data takes no part ; empiricism in ethics like wise does away with the idea of the absolute authority of the moral law as conceived by the intuitionalists. The moral law is merely a collection of rules of conduct based on an infinite number of special cases in which the convenience of society or its rulers has subordinated the inclination of individuals. The funda mental objection to empiricism is that it fails to give an accurate explanation of experience; individual impressions as such are momentary, and their connection into a body of coherent knowl edge presupposes mental action distinct from mere receptivity. Empiricism was characteristic of all early speculation in Greece. During the middle ages the empiric spirit was in abeyance, but it revived from the time of Francis Bacon and was systematized especially by Locke, Hume, the two Mills and Bentham. (See ASSOCIATION OF IDEAS ; METAPHYSICS ; PSYCHOLOGY ; LOGIC.) In medicine, the term is applied to a school of physicians who, in the time of Celsus and Galen, advocated accurate observation of the phenomena of health and disease in the belief that only by the collection of a vast mass of instances would a true science of medicine be attained. This point of view was carried to ex tremes by those who discarded all real study, and based their treatment on rules of thumb. Hence the modern sense of empirical as applied to the guess work of an untrained quack or charlatan.