I am myself convinced that this is the main explanation of the phenomenon: and it is on this conviction that the plan of the present treatise is based. We cannot, of course, regard as valid reasonings that lead to conflicting conclusions; and I therefore assume as a fundamental postulate of Ethics, that so far as two methods conflict, one or other of them must be modified or rejected. But I think it fundamentally important to recognise, at the outset of Ethical inquiry, that there is a diversity of methods applied in ordinary practical thought. § 4. What then are these different methods? what are the different practical principles which the common sense of mankind is _prima facie_ prepared to accept as ultimate? Some care is needed in answering this question: because we frequently prescribe that this or that ‘ought’ to be done or aimed at without any express reference to an ulterior end, while yet such an end is tacitly presupposed. It is obvious that such prescriptions are merely, what Kant calls them, Hypothetical Imperatives; they are not addressed to any one who has not first accepted the end. For instance: a teacher of any art assumes that his pupil wants to produce the product of the art, or to produce it excellent in quality: he tells him that he _ought_ to hold the awl, the hammer, the brush differently. A physician assumes that his patient wants health: he tells him that he _ought_ to rise early, to live plainly, to take hard exercise. If the patient deliberately prefers ease and good living to health, the physician’s precepts fall to the ground: they are no longer addressed to him. So, again, a man of the world assumes that his hearers wish to get on in society, when he lays down rules of dress, manner, conversation, habits of life. A similar view may be plausibly taken of many rules prescribing what are sometimes called “duties to oneself”: it may be said that they are given on the assumption that a man regards his own Happiness as an ultimate end: that if any one should be so exceptional as to disregard it, he does not come within their scope: in short, that the ‘_ought_’ in such formulæ is still implicitly relative to an _optional_ end.