But where the original giving is not upon these terms but avowedly for some return, the most proper course is perhaps for the requital to be such as _both_ shall allow to be proportionate, and, where this cannot be, then for the receiver to fix the value would seem to be not only necessary but also fair: because when the first giver gets that which is equivalent to the advantage received by the other, or to what he would have given to secure the pleasure he has had, then he has the value from him: for not only is this seen to be the course adopted in matters of buying and selling but also in some places the law does not allow of actions upon voluntary dealings; on the principle that when one man has trusted another he must be content to have the obligation discharged in the same spirit as he originally contracted it: that is to say, it is thought fairer for the trusted, than for the trusting, party, to fix the value. For, in general, those who have and those who wish to get things do not set the same value on them: what is their own, and what they give in each case, appears to them worth a great deal: but yet the return is made according to the estimate of those who have received first, it should perhaps be added that the receiver should estimate what he has received, not by the value he sets upon it now that he has it, but by that which he set upon it before he obtained it. Chapter II. Questions also arise upon such points as the following: Whether one’s father has an unlimited claim on one’s services and obedience, or whether the sick man is to obey his physician? or, in an election of a general, the warlike qualities of the candidates should be alone regarded? In like manner whether one should do a service rather to one’s friend or to a good man? whether one should rather requite a benefactor or give to one’s companion, supposing that both are not within one’s power? Is not the true answer that it is no easy task to determine all such questions accurately, inasmuch as they involve numerous differences of all kinds, in respect of amount and what is honourable and what is necessary? It is obvious, of course, that no one person can unite in himself all claims. Again, the requital of benefits is, in general, a higher duty than doing unsolicited kindnesses to one’s companion; in other words, the discharging of a debt is more obligatory upon one than the duty of giving to a companion. And yet this rule may admit of exceptions; for instance, which is the higher duty? for one who has been ransomed out of the hands of robbers to ransom in return his ransomer, be he who he may, or to repay him on his demand though he has not been taken by robbers, or to ransom his own father? for it would seem that a man ought to ransom his father even in preference to himself.