Matthew's Journal

Obviously if you learn something in confidence, you shouldn't pass it on. Sometimes people explicitly say, "This is in confidence", "Just between ourselves", etc. Sometimes it's obvious from the context or subject matter that the information must have been intended to be confidential. On the other hand, if I say something competely anodyne to you or in your presence, I wouldn't mind your passing it on. As usual there's a grey area where there's potential for confusion.

If something is said at a "private party" with, say, 25 people present, the context would suggest to me that a confidence probably wasn't intended, in the absence of any contrary indication. On the other hand, if it was an intimate party, I would expect things to be treated more confidentially.

That still leaves the question of people who overhear remarks by accident (obviously intentionally eavesdropping is bad). They seem to me to be in a slightly different position from the people who are party to the conversation, who have consented to receive the confidence, either expressly or implicitly. In your example, Charlie might be a stranger to you, but very close to Bob. If what you've said was important to Bob (rather than just tittle-tattle), it seems difficult to argue that the course of moral perfection is for Charlie to keep it under his hat.

Editted to correct a couple of typos and to add that sometimes people say foolish things when they're drunk. It's probably best not to repeat such things to those not present.