connotation - First-rate, second-rate, and third-rate

I’d like some clarification on the use of these three words. First-rate has positive connotations and its meaning is manifest, but the meanings of second-rate and third-rate are relatively muddy in comparison.

I know that both of them have negative connotations, and that third-rate is even more forceful in the claim it’s making than is second-rate, but when would it be appropriate to use either?

Is second-rate a better choice of words when doing an explicit comparison like

Prof A is better than Prof B.

When I say Prof B. is second-rate, I’m in fact implying that Prof. B is less than stellar, but not necessarily bottom of the barrel.

And conversely, is third-rate a better choice when making some sort of global claim — like for example, when I say Prof. C is third-rate, I’m implying that he’s the worst, worst professor I’ve ever encountered, and that when Prof. C is juxtaposed with any other professor, he will almost assuredly be found lacking in comparison.

If anybody has insight or clarification on all this, that would be great. And also, if anybody wants to try at the etymology of these three words, then by all means please do so, as I’d be really interested to find out more about their history.

Answer

If you told Prof B that he was second-rate I don't think he'd take any comfort at all from the fact that at least you didn't label him third-rate.

For most purposes, first-rate means "excellent", and both second- and third-rate mean "not good". We actually use second-rate maybe 3-4 times more often than third-rate, but they don't normally both occur in the same utterance unless someone is (somewhat facetiously) saying that something else is even worse than something that was already labelled second-rate.

Historically speaking, third-rate has naval origins - within which context, third-rate ships often actually had the best compromise between sailing ability (speed, handling), firepower, and cost.

But in common parlance no-one thinks like that today - second- and third-rate aren't normally used to indicate different points on the scale of "less than first-rate".