We must make no attempt, therefore, to draw a line of absolute separation between the first two of the three questions in which, as Kant says,[1] all the interests of our reason centre. The "What ought I to do?" of ethics is for ever falling back on the "What can I know?" of metaphysics. The question of practice must accordingly be treated throughout in connection with the question of knowledge. If we use Kant's distinction between speculative and practical reason, we must always bear in mind that it is the same reason which is in one reference speculative, in another practical.[2] We are not at liberty to assume with Butler[3] that "morality ... must be somewhat plain and easy to be understood: it must appeal to what we call common-sense." Nor may we presuppose, as Hutcheson did,[4] that it is a subject "about which a little reflection will discover the truth." The question must be looked upon not so much as one of immediate practical as of scientific interest, and reason is to be regarded as the only court of appeal. [Sidenote: 2. The inquiry into the ethical end] [Sidenote: (_a_) fundamental,] The form just quoted, in which Kant states the problem, is not altogether free from ambiguity. "What ought I to do?" may be taken to signify, What means should I adopt for the attainment of some end presupposed, perhaps unconsciously, as the end to be sought? But it is evident, not only that this is not what Kant himself meant by the question, but that, as thus put, it necessarily implies a further and deeper question. Not the discovery of the means, but the determination of the end itself--the end which cannot be interpreted as a mere means to some further end--is the fundamental question of ethics. It is only by misconception that this can be thought to be a trivial question. To say, as a recent scientific writer does,[5] "that happiness in one disguise or another is the end of human life is common ground for all the schools," is either to ignore what the schools have taught,[6] or else to use the word "happiness" merely as another name for the highest good. But, even were it still the case, as it was in the time of Aristotle, that nearly all men were agreed as to the name of the highest good, and that the common people and the cultured alike called it happiness, the difference as to what they meant by the term would still remain. To say that the ethical end is happiness is, to use Locke's terminology, a "trifling proposition"; for in so doing we merely give it a name[7]--and one which the controversies of philosophy have surrounded with confusion. That the end is happiness in any definite sense, for example, as the greatest balance of pleasure over pain, _may_ be perfectly true, but stands very much in need of proof. That happiness is the highest ethical end can be assumed as true only when "happiness" is nothing more than an abbreviated expression for "the highest ethical end." [Sidenote: (_b_) implies a new point of view,]