There is, however, one practical rule of some value, to be obtained by merely reflecting on the general notion of rightness,[166] as commonly conceived. In a previous chapter[167] I endeavoured to make this notion clearer by saying that ‘what I judge to be right must, unless I am in error, be judged to be so by all rational beings who judge truly of the matter.’ This statement does not imply that what is judged to be right for one man must necessarily be judged so for another: ‘objective’ rightness may vary from _A_ to _B_ no less than the ‘objective’ facts of their nature and circumstances vary. There seems, however, to be this difference between our conceptions of ethical and physical objectivity respectively: that we commonly refuse to admit in the case of the former--what experience compels us to admit as regards the latter--variations for which we can discover no rational explanation. In the variety of coexistent physical facts we find an accidental or arbitrary element in which we have to acquiesce, as we cannot conceive it to be excluded by any extension of our knowledge of physical causation. If we ask, for example, why any portion of space empirically known to us contains more matter than any similar adjacent portion, physical science can only answer by stating (along with certain laws of change) some antecedent position of the parts of matter which needs explanation no less than the present; and however far back we carry our ascertainment of such antecedent positions, the one with which we leave off seems as arbitrary as that with which we started. But within the range of our cognitions of right and wrong, it will be generally agreed that we cannot admit a similar unexplained variation. We cannot judge an action to be right for _A_ and wrong for _B_, unless we can find in the natures or circumstances of the two some difference which we can regard as a reasonable ground for difference in their duties. If therefore I judge any action to be right for myself, I implicitly judge it to be right for any other person whose nature and circumstances do not differ from my own in some important respects. Now by making this latter judgment explicit, we may protect ourselves against the danger which besets the conscience, of being warped and perverted by strong desire, so that we too easily think that we ought to do what we very much wish to do. For if we ask ourselves whether we believe that any similar person in similar circumstances ought to perform the contemplated action, the question will often disperse the false appearance of rightness which our strong inclination has given to it. We see that we should not think it right for another, and therefore that it cannot be right for us. Indeed this test of the rightness of our volitions is so generally effective, that Kant seems to have held that all particular rules of duty can be deduced from the one fundamental rule “Act as if the maxim of thy action