Is it possible for a man to act unjustly toward himself (e.g., is the man who commits suicide or mutilates himself guilty of an injustice to himself)? In their truest senses, justice and injustice pertain only to social relations and dealings between men. Someone other than the agent is required as a subject, and one can only be unjust to someone other than himself. At most, suicide and related acts must be viewed as crimes against society or the state.
There is, however, one sense in which a man may commit a form of injustice toward himself. In the Republic, Plato drew a distinction between the rational and irrational parts of the soul. He said that justice of the soul is a harmony between these parts, in which each performs its proper function under control of reason. In his view, injustice of the soul occurs when one part thwarts or frustrates the legitimate desires of the other part. Thus, in a metaphorical sense, it is possible to say that a man can be guilty of injustice toward himself, meaning that he allows his irrational part to dominate his rational part. But this is not real injustice; this harmony between a man's inner elements is analogous to "justice" between master and slave or head of household and family, which were discussed earlier under the heading of "domestic justice."
Aristotle's conception of justice as explained above has had an immense influence on medieval and modern jurisprudence. It is important to note, however, that Aristotle is dealing in Book V with justice in a restricted sense. He is more concerned with human relations and individual obligations in the polis or city-state than with the formulation of legal codes and the operation of judicial systems. Some critics have asserted that Aristotle's discussion of justice is confusing because of his attempt to describe it according to a mathematical formula.