I'm brand new to classical music and music theory. I often see something for a concert like "brandenburg concerto no. 2 in f major". Why do we specify f major? Once we've specified brandenburg concerto no. 2 haven't we fully specified the piece. I mean it is not as if there is an option to change the signature key is there? When I buy a truck I don't say Ford F150 with an engine so what is going on with music?
Thanks, Scott
Musicians form much closer relationships with keys than with arbitrary numbers. I might not remember which Brandenburg Concerto is which by the numbers, but listing the key really clues me in. This is especially true for composers who wrote a ton of a single type of piece, for example Mozart's piano sonatas or Haydn's symphonies.
Music can and often is transposed to other keys. Sometimes this is done for vocalists who want to be able to sing a song within their range. In classical music it may be a case of the instrumentation in the ensemble that will be performing the piece. Some instruments are easier to play in one key than in another.
Regardless of the reason for transposing (changing) a piece to a different key, the fact remains that it can be done and it is not uncommon to do so. Many classical pieces are traditionally played in the key they were composed in/for. But even those could theoretically be performed in another key. So to remove any doubt, it's best to announce the key - primarily for the sake of the musicians.
As for your F-150 Truck analogy - if the truck was offered in different engines you might say "I want the F-150 with the 2.7 Litre Eco Boost V6 instead of the F-150 with the 5.0 Litre V8. But a another analogy would be that you can buy a Ford F-150 Pickup Truck and it will be a Ford F-150. But you could get it in Red, Black, Blue, White, Silver or Maroon. So you might want to specify the color.
I'm tempted to suggest that this practice actually far predates the creation of keys. I believe Renaissance and Medieval church pieces were often categorized by which of the 8 Church Modes they were written in. This would tell a church musician a lot about the mood, or ethos, of the piece, and aid the singers in knowing what scale to use. Speculating... it may also have suggested other pieces in similar (or contrasting) moods that could be arranged with it. In short, a piece's identity had much to do with it's mode -- much like how a book's genre determines much of its linguistic form and content.
Later, when music shifted from modes to keys, there was some initial confusion (at least by some) about the difference between the two systems, but at any rate, it made sense to keep referring to pieces by their tonality. Once again, a piece's key was closely tied to it's character. Especially in the days before equal temperament, when different keys were considered to have different characters.
Another consideration is that composers often didn't bother naming or numbering their own works -- for example, the Brandenburg Concertos were actually merely titled "Six Concertos for Several Instruments". So any system that can distinguish between two pieces is fair game. This includes listing the form (e.g. "Concerto"), the key (e.g. "in F Major"), and the instrumentation (e.g. "for Trumpet, Recorder, Oboe, Violin, Strings, and Continuo"). Together with the composer's name (e.g. "by J. S. Bach"), this is often enough to identify the specific piece, or at least narrow down the possibilities significantly. Even when pieces are explicitly numbered, these other factors are more meaningful than an arbitrary number.
You'll notice that when pieces do have a specific name, the key designation is used considerably less: Vivaldi's "Spring" vs. "Violin Concerto in E Major"; Beethoven's "Choral Symphony" vs. "Symphony No. 9 in D Major"; Sousa's "Stars and Stripes Forever" vs. "March in ... whatever key Stars and Stripes is in..."
