And this is universally true of ‘particular’ and ‘general,’ when used in this common, but inaccurate, sense. So far as Ethics allows itself to give lists of virtues or even to name constituents of the Ideal, it is indistinguishable from Casuistry. Both alike deal with what is general, in the sense in which physics and chemistry deal with what is general. Just as chemistry aims at discovering what are the properties of oxygen, _wherever it occurs_, and not only of this or that particular specimen of oxygen; so Casuistry aims at discovering what actions are good, _whenever they occur_. In this respect Ethics and Casuistry alike are to be classed with such sciences as physics, chemistry and physiology, in their absolute distinction from those of which history and geography are instances. And it is to be noted that, owing to their detailed nature, casuistical investigations are actually nearer to physics and to chemistry than are the investigations usually assigned to Ethics. For just as physics cannot rest content with the discovery that light is propagated by waves of ether, but must go on to discover the particular nature of the ether-waves corresponding to each several colour; so Casuistry, not content with the general law that charity is a virtue, must attempt to discover the relative merits of every different form of charity. Casuistry forms, therefore, part of the ideal of ethical science: Ethics cannot be complete without it. The defects of Casuistry are not defects of principle; no objection can be taken to its aim and object. It has failed only because it is far too difficult a subject to be treated adequately in our present state of knowledge. The casuist has been unable to distinguish, in the cases which he treats, those elements upon which their value depends. Hence he often thinks two cases to be alike in respect of value, when in reality they are alike only in some other respect. It is to mistakes of this kind that the pernicious influence of such investigations has been due. For Casuistry is the goal of ethical investigation. It cannot be safely attempted at the beginning of our studies, but only at the end. =5.= But our question ‘What is good?’ may have still another meaning. We may, in the third place, mean to ask, not what thing or things are good, but how ‘good’ is to be defined. This is an enquiry which belongs only to Ethics, not to Casuistry; and this is the enquiry which will occupy us first.