Objection 1: It would seem that "paternal right" and "right of dominion" should not be distinguished as special species. For it belongs to justice to render to each one what is his, as Ambrose states (De Offic. i, 24). Now right is the object of justice, as stated above (A. 1). Therefore right belongs to each one equally; and we ought not to distinguish the rights of fathers and masters as distinct species.
Obj. 2: Further, the law is an expression of what is just, as stated above (A. 1, ad 2). Now a law looks to the common good of a city or kingdom, as stated above (I-II, Q. 90, A. 2), but not to the private good of an individual or even of one household. Therefore there is no need for a special right of dominion or paternal right, since the master and the father pertain to a household, as stated in Polit. i, 2.
Obj. 3: Further, there are many other differences of degrees among men, for instance some are soldiers, some are priests, some are princes. Therefore some special kind of right should be allotted to them.
On the contrary, The Philosopher (Ethic. v, 6) distinguishes right of dominion, paternal right and so on as species distinct from civil right.
I answer that, Right or just depends on commensuration with another person. Now "another" has a twofold signification. First, it may denote something that is other simply, as that which is altogether distinct; as, for example, two men neither of whom is subject to the other, and both of whom are subjects of the ruler of the state; and between these according to the Philosopher (Ethic. v, 6) there is the "just" simply. Secondly a thing is said to be other from something else, not simply, but as belonging in some way to that something else: and in this way, as regards human affairs, a son belongs to his father, since he is part of him somewhat, as stated in Ethic. viii, 12, and a slave belongs to his master, because he is his instrument, as stated in Polit. i, 2 [*Cf. Ethic. viii, 11]. Hence a father is not compared to his son as to another simply, and so between them there is not the just simply, but a kind of just, called "paternal." In like manner neither is there the just simply, between master and servant, but that which is called "dominative." A wife, though she is something belonging to the husband, since she stands related to him as to her own body, as the Apostle declares (Eph. 5:28), is nevertheless more distinct from her husband, than a son from his father, or a slave from his master: for she is received into a kind of social life, that of matrimony, wherefore according to the Philosopher (Ethic. v, 6) there is more scope for justice between husband and wife than between father and son, or master and slave, because, as husband and wife have an immediate relation to the community of the household, as stated in Polit. i, 2, 5, it follows that between them there is "domestic justice" rather than "civic."
Reply Obj. 1: It belongs to justice to render to each one his right, the distinction between individuals being presupposed: for if a man gives himself his due, this is not strictly called "just." And since what belongs to the son is his father's, and what belongs to the slave is his master's, it follows that properly speaking there is not justice of father to son, or of master to slave.
Reply Obj. 2: A son, as such, belongs to his father, and a slave, as such, belongs to his master; yet each, considered as a man, is something having separate existence and distinct from others. Hence in so far as each of them is a man, there is justice towards them in a way: and for this reason too there are certain laws regulating the relations of father to his son, and of a master to his slave; but in so far as each is something belonging to another, the perfect idea of "right" or "just" is wanting to them.
Reply Obj. 3: All other differences between one person and another in a state, have an immediate relation to the community of the state and to its ruler, wherefore there is just towards them in the perfect sense of justice. This "just" however is distinguished according to various offices, hence when we speak of "military," or "magisterial," or "priestly" right, it is not as though such rights fell short of the simply right, as when we speak of "paternal" right, or right of "dominion," but for the reason that something proper is due to each class of person in respect of his particular office.