The real turning point between morality and simple expediency is contained in the penal sanction.  Duty is what we may exact of a person; there may be reasons why we do not exact it, but the person himself would not be entitled to complain if we did so.  Expediency, on the other hand, points to things that we may wish people to do, may praise them for doing, and despise them for not doing, while we do not consider it proper to bring in the aid of punishment.

There enters farther into the idea of Justice what has been expressed by the ill-chosen phrase, ‘perfect obligation,’ meaning that the duty involves a moral right on the part of some definite person, as in the case of a debt; an imperfect obligation is exemplified by charity, which gives no legal claim to any one recipient.  Every such right is a case of Justice, and not of Beneficence.

The Idea of Justice is thus shown to be grounded in Law; and the next question is, does the strong feeling or sentiment of Justice grow out of considerations of utility?  Mr. Mill conceives that though the notion of expediency or utility does not give birth to the sentiment, it gives birth to what is moral in it.

The two essentials of justice are (1) the desire to punish some one, and (2) the notion or belief that harm has been done to some definite individual or individuals.  Now, it appears to the author that the desire to punish is a spontaneous outgrowth of two sentiments, both natural, and, it may be, instinctive; the impulse of self-defence, and the feeling of sympathy.  We naturally resent, repel, and retaliate, any harm done to ourselves and to any one that engages our sympathies.  There is nothing moral in mere resentment; the moral part is the subordination of it to our social regards.  We are moral beings, in proportion as we restrain our private resentment whenever it conflicts with the interests of society.  All moralists agree with Kant in saying that no act is right that could not be adopted as a law by all rational beings (that is, consistently with the well-being of society).

There is in Justice a rule of conduct, and a right on the part of some one, which right ought to be enforced by society.  If it is asked why society ought to enforce the right, there is no answer but the general utility.  If that expression seem feeble and inadequate to account for the energy of retaliation inspired by injustice, the author asks us to advert to the extraordinarily important and impressive kind of utility that is concerned.  The interest involved is security, to every one’s feelings the most vital of all interests.  All other earthly benefits needed by one person are not needed by another; and many of them can, if necessary, be cheerfully foregone, or replaced by something else; but security no human being can possibly do without; on it we depend for all our immunity from evil, and for the whole value of all and every good, beyond the passing moment.