20. At any one of these steps of Induction in the Table, the inductive proposition is a _Theory_ with regard to the Facts which it includes, while it is to be looked upon as a _Fact_ with respect to the higher generalizations in which it is included. In any other sense, as was formerly shown, the opposition of _Fact_ and _Theory_ is untenable, and leads to endless perplexity and debate. Is it a Fact or a Theory that the planet Mars revolves in an Ellipse about the Sun? To Kepler, employed in endeavouring to combine the separate observations by the Conception of an Ellipse, it is a Theory; to Newton, engaged in inferring the law of force from a knowledge of the elliptical motion, it is a Fact. There are, as we have already seen, no special attributes of Theory and Fact which distinguish them from one another. Facts are phenomena apprehended by the aid of conceptions and mental acts, as Theories also are. We commonly call our observations _Facts_, when we apply, without effort or consciousness, conceptions perfectly familiar to us: while we speak of Theories, when we have previously contemplated the Facts and the connecting Conception separately, and have made the connexion by a conscious mental act. The real difference is a difference of relation; as the same proposition in a demonstration is the _premiss_ of one syllogism and the _conclusion_ in another;--as the same person is a father and a son. Propositions are Facts and Theories, according as they stand above or below the Inductive Brackets of our Tables. 21. To obviate mistakes I may remark that the terms _higher_ and _lower_, when used of generalizations, are unavoidably represented by their opposites in our Inductive Tables. The highest generalization is that {117} which includes all others; and this stands the lowest on our page, because, reading downwards, that is the place which we last reach. There is a distinction of the knowledge acquired by Scientific Induction into two kinds, which is so important that we shall consider it in the succeeding chapter. {{118}} CHAPTER VII. OF LAWS OF PHENOMENA AND OF CAUSES. APHORISM XXIV. _Inductive truths are of two kinds_, Laws of Phenomena, _and_ Theories of Causes. _It is necessary to begin in every science with the Laws of Phenomena; but it is impossible that we should be satisfied to stop short of a Theory of Causes. In Physical Astronomy, Physical Optics, Geology, and other sciences, we have instances showing that we can make a great advance in inquiries after true Theories of Causes._