relations of the family, friendship varies with the different situations.  Parents love their children as a part of themselves, and from the first; children grow to love their parents.  Brothers are affected by their community of origin, as well as by common education and habits of intimacy.  Husband and wife come together by a natural bond, and as mutual helps; their friendship contains the useful and the pleasant, and, with virtue, the good.  Their offspring strengthens the bond (XII.).  The friendships that give rise to complaints are confined to the Useful.  Such friendships involve a legal element of strict and measured reciprocity [mere trade], and a moral or unwritten understanding, which is properly friendship.  Each party is apt to give less and expect more than he gets; and the rule must be for each to reciprocate liberally and fully, in such manner and kind as they are able (XIII.).  In unequal friendships, between a superior and inferior, the inferior has the greater share of material assistance, the superior should receive the greater honour (XIV.).

Book Ninth proceeds without any real break.  It may not be always easy to fix the return to be made for services received.  Protagoras, the sophist, left it to his pupils to settle the amount of fee that he should receive.  When there is no agreement, we must render what is in our power, for example, to the gods and to our parents (I.).  Cases may arise of conflicting obligation; as, shall we prefer a friend to a deserving man? shall a person robbed reciprocate to robbers? and others. [We have here the germs of Casuistry.] (II.) As to the termination of Friendship; in the case of the useful and the pleasant, the connexion ceases with the motives.  In the case of the good, it may happen that one party counterfeits the good, but is really acting the useful or the pleasant; or one party may turn out wicked, and the only question is, how far hopes of his improvement shall be entertained.  Again, one may continue the same, while the other makes large advances in mental training; how far shall present disparity operate against old associations? (III.).  There is a sort of illustrative parallelism between the feelings and acts of friendship, and the feelings and acts of self-love, or of a good man to himself.  The virtuous man wishes what is good for himself, especially for his highest part—­the intellect or thinking part; he desires to pass his life in the company of his own thoughts; he sympathizes with his own sorrows.  On the other hand, the bad choose the pleasant, although it be hurtful; they fly from themselves; their own thoughts are unpleasant companions; they are full of repentance (IV.).  Good-will is different from friendship; it is a sudden impulse of feeling towards some distinguished or likeable quality, as in an antagonist.  It has not the test of longing in absence.  It may be the prelude to friendship (V.).  Unanimity, or agreement of opinion, is a part of friendship.  Not as regards mere speculation, as about the heavenly bodies; but in practical matters, where interests are at stake, such as the politics of the day.  This unanimity cannot occur in the bad, from their selfish and grasping disposition (VI.).