I don’t know if I’m stupid or not, but I guess I’m pretty unobservant. I think.
One of my favorite piece of music (hell, I told my daughter that it was a “towering achievement of Western Civilization” so I guess I like it a lot) is the 2nd Brandenburg, especially the 3rd movement (yeah, I’m a walking cliche. So sue me).
So I’m listening to the concerto again this morning, and I realize: Dammit, this thing is a fugue! :smack: I’ve only been familiar with the piece for, oh, maybe 15 years or more. :rolleyes:
Then I listen further with the fugue idea in mind: Well, maybe not.
But I don’t know/remember enough about music structure to say for sure. It’s definitely polyphonic, but since we’re talking about Bach here, that’s akin to saying “that water is definitely wet.” 
So… is it a fugue?