The stock example of a semantic tautology is that all bachelors are unmarried. It is supposed to be immediately obvious and necessarily true. It seems to me, however, that it is neither immediately obvious nor necessary.
That it is not immediately obvious: Bachelor is not a word I use much, outside of repeating the stock example of a tautology, and the stock example is so well-worn with repetition that I don’t find it resonates with me. I say it automatically, rather than with conviction.
This is also my experience when teaching (e.g.) “Two Dogmas of Empiricism” to undergraduates. It’s Quine, so their eyes go glassy a bit anyway, but the example doesn’t seem to resonate much with them. Most of them learn to repeat it, but neither they nor I say it with the passion of lively belief.
That it is not necessary: When I use the word bachelor outside the classroom, the context is someone who lives a particular lifestyle. Their bachelor pad is a cluttered apartment, their schedule and time are largely their own, and they either flit from relationship to relationship or are resolutely single.
Imagine someone who matches that description; call him Bachman. Suppose he enters into an arrangement with someone who would benefit from being married for logistical reasons, perhaps for health insurance or for immigration reasons. Bachman signs paperwork and is married, but continues to live his life just as he has done before. He still lives the life of a bachelor. It seems to me that one can consistently say, “Bachman is a bachelor who is married.”
Alternately, imagine the unhappily married Marvin who separates from his spouse. He gets his own place, sleeps around, and lives his own life. His spouse moves far away and doesn’t keep in touch. Marvin lives the life of a bachelor, even though he has not actually divorced. It seems to me that one can consistently say, “Marvin is a bachelor who is married.”
If you think that these sentences should get an asterisk next to them, replace “married” with “legally married”. It seems obvious to me that someone can be a bachelor even though they are legally married. And it also seems tautological that someone is married if they are legally married.
These usages might be taken to show that “bachelor” and “married” are property clusters, but maybe not. “Married” at least breaks down into the separate components of being legally bound together and being in the shared project of living a life together. Bachman and Marvin are married in the first sense but not in the latter.