a single name, to recognise them, to discourse about them. This would be impossible if the severality were not veiled or hidden by unitive likeness.

46. Science is either theoretic or practical. A theory is an explanation-an explanatory thesis or a system of explanatory theses. Theoretic science is science that is explanatory, e.g. geometry, geology. Practical science is knowledge of a system of rules respecting means available to man. Arithmetic, logic, rhetoric, and the sciences of painting and shoemaking, are examples of practical science. Certain sciences are compounds of theoretical and practical sciences. Logic is such a compound, and has consequently occasioned controversy as to whether it be a theoretic or a practical science. Practical science has never been adequately discriminated from art, nor art from skill. These it is necessary to define in order to rescue the idea of science from partial confusion. Skill is power to do felicitously what the agent intends. It is either congenital or acquired. Congenital skill is strikingly manifested in the insect world. Acquired skill is either regular or irregular, the former when it does, the latter when it does not, consciously proceed on rule or result from such proceeding. Skill in hitting the mark is an example of irregular skill. It results from practice unaided by rule. It is incommunicable by words. A certain dyer endowed with extraordinary skill in compounding his ingredients was ignorant of the rule according to which his acquired skill proceeded. Irregular skill whether congenital or acquired is the source of all regular skill. Homer working according to unknown rules produced in the Iliad manifestations of poetic rule which contributed to engender the art of

poetry and enabled Virgil to apply regular skill in the production of the Eneid. Art is regular skill developed by practical science.1 Practical science is essential to art, but the converse is not true: art is not essential to

practical science. One might know every rule in arithmetic and be unable to do a sum. Paralysis might deprive a painter of his skill and not of knowledge of the rules of his art. Note that explanatoriness, not privation of action, is the differentia of theoretic science. In its conscious state practical science no more involves action than theoretic science. An arithmetician revolving in his mind the rules of his science without applying them in calculation is as purely contemplative -as absorbed in discernment unconnected with action -as the geometrician revolving his theorems. Neither the skill nor the action of which a practical science is the condition is essential to its conscious state: the ideas of the skill and the action are essential to it, but neither the skill nor the action. Practical science is practical not in the sense that its discernment, like that of looking, listening, or scrutiny of any kind, is involved with action, but that its cognitum-what it discerns consists of practical rules. A reference to the seventh of Sir William Hamilton's Lectures on Metaphysics will show that the ground or reason of my division of science into theoretic and practical is different from that of Aristotle; that I charge the word "theoretic" with a meaning which Aristotle ignored, viz. explanatoriness, and that I bring to the front a face o

1 Dr. Whewell mistakes irregular skill for art. "Art," he says, "is the parent, not the progeny of science." Irregular skill is indeed the parent, not of all science but, of practical science, and through science of art it is the parent of practical science and the grandfather of art. See History of the Inductive Sciences, Book iv. chap. v.

the connotation of the word "practical" which he had not in view. The change puts in bright relief the difference between science and art which, had it been visible to Seneca, would have exempted him from the error, that philosophy is active as well as contemplative. Philosophia et contemplativa est et activa: spectat simulque agit. It is art, not science, that is active— that has action involved with discernment. The confusion of art with science, by the way, has been favoured by the ambiguity of the names of practical sciences: they denote not only the sciences, but also the corresponding arts.

CLXIII.

Scientific knowledge may be either thorough or short of thoroughness. It is thorough when it is knowledge of all that is humanly known respecting its system of theses. Thoroughness does not suppose absence of defect. Every science is defective. When the mind is so related to geometry that it can, at will, bring before it the evidence of every geometrical proposition, its geometrical knowledge is thorough. But thorough geometrical knowledge is rare, even among mathematicians. The rungs on which they scale the mathematical heights tend to give way when they are no longer used. But that mathematicians are not able to muster geometrical evidence at will, does not suppose them to be ignorant of geometry. Their knowledge of geometry is not thorough but it is scientific, and, in spite of the defect of thoroughness, it is sufficient as a foundation.

1 Seneca, Epist. xcv.

A young physician fresh from the schools usually has a better knowledge of anatomy and physiology than old and able practitioners. His knowledge of those sciences may be thorough and theirs is not.

CLXIV.

Certainty objective to scientific discernment short of thoroughness seems to differ intrinsically from certainty caused by authority or by inference from the belief of others. Contrast the certainty which a geometrical thesis exhibits to one who has studied, but has forgotten, the demonstration, with that which it exhibits to a person who has inferred its truth from the belief of others. Both discernments refer to the same object and to nothing beside; neither refers to the evidence from which it sprang; yet one of the certainties seems to differ from the other so as to make its discernment scientific, to impart to it an aspect of certitude, whereas the other confers no such aspect. It is true then that certainties, in spite of their seeming simplicity, may differ from one another as to quality, and that the corresponding certitudes differ in like manner.

CHAPTER II.

DEDUCTION OF AN UNCONSCIOUS PART OF THE MIND AND OF UNCONSCIOUS MENTAL EVENT.

CLXV.

THAT the human mind includes an unconscious part,one of which it is unintuitive, that unconscious events, occurring in that part and partly determined by its structure, are proximate causes of consciousness, that the greater part of human intentional action is an effect of an unconscious cause,-the truth of these propositions is deducible from ordinary mental event, and is so near the surface that the failure of deduction to forestall induction in the discovery of it may well excite wonder. And of what transcendent importance is the fact which familiar events were importunate to signify to deduction, no less than this, that an unconscious part of the mind bears to a part of consciousness such a relation as the magic lantern bears to the luminous disc which it projects, that the greater part of intentional action, the greater part of what is mistaken for volition, in fact, the whole practical life of the vast majority of men, is an effect of event as remote from consciousness as fermentation, vegetable growth, or the motions of the planets. Coupled with physiological induction, it