definition. Such evidence must contain propositions of two kinds and of two kinds only: it must consist, in the first place, of truths with regard to the results of the action in question—of causal truths—but it must also contain ethical truths of our first or self-evident class. Many truths of both kinds are necessary to the proof that any action ought to be done; and any other kind of evidence is wholly irrelevant. It follows that, if any ethical philosopher offers for propositions of the first kind any evidence whatever, or if, for propositions of the second kind, he either fails to adduce both causal and ethical truths, or adduces truths that are neither, his reasoning has not the least tendency to establish his conclusions. But not only are his conclusions totally devoid of weight: we have, moreover, reason to suspect him of the error of confusion; since the offering of irrelevant evidence generally indicates that the philosopher who offers it has had before his mind, not the question which he professes to answer, but some other entirely different one. Ethical discussion, hitherto, has perhaps consisted chiefly in reasoning of this totally irrelevant kind.
One main object of this book may, then, by expressed by slightly changing one of Kant’s famous titles. I have endeavoured to write ‘Prolegomena to any future Ethics that can possibly pretend to be scientific.’ In other words, I have endeavoured to discover what are the fundamental principles of ethical reasoning; and the establishment of these principles, rather than of any conclusions which may be attained by their use, may be regarded as my main object. I have, however, also attempted, in Chapter VI, to present some conclusions, with regard to the proper answer to the question, ‘What is good in itself?’ which are very different from any which have commonly been advocated by philosophers. I have tried to define the classes within which all great goods and evils fall; and I have maintained that very many different things are good and evil
