The private vs. public divide used to be relatively straightforward: things remained private unless you disclosed them to someone, either deliberately or accidentally — but even in the case of accidental disclosure, there was no way for your information to reach the entire planet unless it appeared on the evening news. Now, a tweet or a photo or a status update could suddenly appear on a news website, or be retweeted thousands of times, or be used as evidence of some pernicious social phenomenon you may never even have heard of before.

But you posted those things, so they must be public, right? And because they are public, any use of them is permitted, right?

A universe filled with nuance and slippery ethical slopes is contained in those questions. And while many of us have gotten used to the back-and-forth with Facebook (s fb) over what is private and…