The equality implied in justice is therefore to be understood as an exclusion of the irrelevant, and thus supposes an understanding as to what is irrelevant. It is not a mere abstract assertion of equality; but the assertion that, in a given concrete case, a certain rule is to be applied without considering anything outside of the rule. An ideally perfect rule would contain within itself a sufficient indication of what is to be relevant. All men of full age, sound mind, and so forth, are to be treated in such and such a way. Then all cases falling within the rule are to be decided on the same principles, and in that sense equally. But the problem remains, what considerations should be taken into account by the rule itself? Let us put the canon of equality in a different shape, namely, that there should always be a sufficient reason for any difference in the treatment of our fellows. This rule does not imply that I should act in all cases as though all men were equal in character or mind, but that my action should in all cases be justified by some appropriate consideration. It does not prove that every man should have a vote, but that if one man has a vote and another has not, there should be some adequate reason for the difference. It does not prove that every man should work eight hours a day and have a shilling an hour; but that differences of hours or of pay and, equally, uniformity of hours and pay, should have some sufficient justification. This is a deeper principle, which in some cases justifies and in others does not justify the rule of equality. The rule of equality follows from it under certain conditions, and has gained credit because, in point of fact, those conditions have often been satisfied.