of mere preference of one child to another. Yet in the case of
primogeniture our opinion would have to be modified. Supposing, for
example, a state of society in which primogeniture was generally
recognised as desirable for public interests, we could hardly call a
man unjust for leaving his estates to his eldest son. If, in such a
state, a man breaks the general rule, our judgment of his conduct would
be determined perhaps by considering whether he was before or behind
his age, whether he was acting from a keener perception of the evils of
inequality or actuated by spite or regardless of the public interests
which he believed to be concerned. A parent treats his children equally
in his will in regard to money; but he does not, unless he is a fool,
give the same training or the same opening to all his children, whether
they are stupid or clever, industrious or idle. But what I wish to
insist upon is, that justice implies essentially indifference to
irrelevant considerations, and therefore, in many cases, equality in
the treatment of the persons concerned. A judge has to decide without
reference to bribes, and not be biassed by the position of an accused
person. In that sense he treats the men equally, but of course he does
not give equal treatment to the criminal and innocent, to the rightful
and wrongful claimant.

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 sho