Samuel Johnson refers to Michel de Montaigne in Essay no 13 of The Rambler. May 1st. 1750. In an aside on the keeping and the telling of the secrets of others entrusted to one he writes:
There have, indeed, been some enthusiastick and irrational zealots for friendship, who have maintained, and perhaps believed, that one friend has a right to all that is in possession of another; and that therefore it is a violation of kindness to exempt any secret from this boundless confidence. Accordingly a late female minister of state has been shameless enough to inform the world, that she used, when she wanted to extract any thing from her sovereign, to remind her of Montaigne's reasoning, who has determined, that to tell a secret to a friend is no breach of fidelity, because the number of persons trusted is not multiplied, a man and his friend being virtually the same.
That such a fallacy could be imposed upon any human understanding, or that an author could have advanced a position so remote from truth and reason, any otherwise than as a declaimer, to shew to what extent he could stretch his imagination, and with what strength he could press his principle, would scarcely have been credible, had not this lady kindly shewn us how far weakness may be deluded, or indolence amused.
I am, with Johnson, against Montaigne's airy man of the world sharing and my own way with the secrets of others is to forget them as quickly as possible. Am I an abyss of discretion? I am not at liberty to disclose but I will say this... No better not. Have you ever met friends of a friend that you haven't met before and sensed the presence of forward intelligence that may not be altogether benign. They being forewarned and forearmed creates a blockade. Is this just paranoia? The common rationalisation that not gossiping is a sign of a lack of interest in people is destructive of friendship and you can be certain that you too will be served as a piquant dip.
The rules therefore that I shall propose concerning secrecy, and from which I think it not safe to deviate, without long and exact deliberation, are—Never to solicit the knowledge of a secret. Not willingly, nor without many limitations, to accept such confidence when it is offered. When a secret is once admitted, to consider the trust as of a very high nature, important as society, and sacred as truth, and therefore not to be violated for any incidental convenience, or slight appearance of contrary fitness.
I am taking two shots of The Rambler every day and besides the grandiloquence of the stately periods, his profound moral sense and seriousness blended with a realisation of personal fallibility does me good.
Addendum: As I suspected the Montaigne essay that Johnson refers to is De L’Amitie or On Friendship or by Screech On Affectionate Relationships
If one (of two friends) entrusted to your silence something which it was useful for the other to know, how would you get out of that? The unique, highest friendship loosens all other bonds. That secret which I have sworn to reveal to no other, I can reveal without perjury to him who is not another: he is me. It is a great enough miracle for oneself to be redoubled: they do not realize how high a one it is when they talk of its being tripled.(Screech trans.)