It is natural that a man should first incur an obligation, and then that he should return gratitude for it; a debtor cannot exist without a creditor, any more than a husband without a wife, or a son without a father; someone must give in order that someone may receive. Just as no one carries himself, although he moves his body and transports it from place to place; as no one, though he may have made a speech in his own defence, is said to have stood by himself, or erects a statue to himself as his own patron; as no sick man, when by his own care he has regained his health, asks himself for a fee; so in no transaction, even when a man does what is useful to himself, need he return thanks to himself, because there is no one to whom he can return them. Though I grant that a man can bestow a benefit upon himself, yet at the same time that he gives it, he also receives it; though I grant that a man may receive a benefit from himself, yet he receives it at the same time that he gives it. The exchange takes place within doors, as they say, and the transfer is made at once, as though the debt were a fictitious one; for he who gives is not a different person to he who receives, but one and the same.