12.  But since it appears, that even this sophistry has been able, with the help of a strong desire to repose in quiet upon the understanding of another, to mislead honest intentions, and an understanding not contemptible, it may not be superfluous to remark, that those things which are common among friends are only such as either possesses in his own right, and can alienate or destroy without injury to any other person.  Without this limitation, confidence must run on without end, the second person may tell the secret to the third upon the same principle as he received it from the first, and the third may hand it forward to a fourth, till at last it is told in the round of friendship to them from whom it was the first intention chiefly to conceal it.

13.  The confidence which Caius has of the faithfulness of Titius is nothing more than an opinion which himself cannot know to be true, and which Claudius, who first tells his secret to Caius, may know, at least may suspect to be false; and therefore the trust is transferred by Caius, if he reveal what has been told him, to one from whom the person originally concerned would probably have withheld it; and whatever may be the event, Caius has hazarded the happiness of his friend, without necessity and without permission, and has put that trust in the hand of fortune was given only to virtue.

14.  All the arguments upon which a man who is telling the private affairs of another may ground his confidence in security, he must upon reflection know to be uncertain, because he finds them without effect upon himself.  When he is imagining that Titius will be cautious from a regard to his interest, his reputation, or his duty, he ought to reflect that he is himself at that instant acting in opposition to all these reasons, and revealing what interest, reputation and duty direct him to conceal.

15.  Every one feels that he should consider the man incapable of trust, who believed himself at liberty to tell whatever he knew to the first whom he should conclude deserving of his confidence:  therefore Caius, in admitting Titius to the affairs imparted only to himself, violates his faith, since he acts contrary to the intention of Claudius, to whom that faith was given.  For promises of friendship are, like all others, useless and vain, unless they are made in some known sense, adjusted and acknowledged by both parties.

16.  I am not ignorant that many questions may be started relating to the duty of secrecy, where the affairs are of public concern; where subsequent reasons may arise to alter the appearance and nature of the trust; that the manner in which the secret was told may change the degree of obligation; and that the principles upon which a man is chosen for a confidant may not always equally constrain him.

17.  But these scruples, if not too intricate, are of too extensive consideration for my present purpose, nor are they such as generally occur in common life; and though casuistical knowledge be useful in proper hands, yet it ought by no means to be carelessly exposed, since most will use it rather to lull than awaken their own consciences; and the threads of reasoning, on which truth is suspended, are frequently drawn to such subtility, that common eyes cannot perceive, and common sensibility cannot feel them.