answer, but which, as I have tried to shew, they have almost always confused both with one another and with other questions. These two questions may be expressed, the first in the form: What kind of things ought to exist for their own sakes? the second in the form: What kind of actions ought we to perform? I have tried to shew exactly what it is that we ask about a thing, when we ask whether it ought to exist for its own sake, is good in itself or has intrinsic value; and exactly what it is that we ask about an action, when we ask whether we ought to do it, whether it is a right action or duty.
But from a clear insight into the nature of these two questions, there appears to me to follow a second most important result: namely, what is the nature of the evidence, by which alone any ethical proposition can be proved or disproved, confirmed or rendered doubtful. Once we recognize the exact meaning of the two questions, I think it also becomes plain exactly what kind of reasons are relevant as arguments for or against any particular answer to them. It becomes plain that, for answers to the first question, no relevant evidence whatever can be adduced: from no other truth, except themselves alone, can it be inferred that they are either true or false. We can guard against error only by taking care, that, when we try to answer a question of this kind, we have before our minds that question only, and not some other or others; but that there is great danger of such errors of confusion I have tried to shew, and also what are the chief precautions by the use of which we may guard against them. As for the second question, it becomes equally plain, that any answer to it is capable of proof or disproof—that, indeed, so many different considerations are relevant to its truth or falsehood, as to make the attainment of probability very difficult, and the attainment of certainty impossible. Nevertheless the kind of evidence, which is both necessary and alone relevant to such proof and disproof, is capable of exact
