It's a C# diminished triad. If the composer didn't want an A in there, then he didn't want an A7.
I understand that functionally it can perform the job an A7 chord performs, but it's not an A7.
I agree with you up to this point...
...but here I disagree.
Yes, the rules get broken all the time by people but if we all have a different set of rules, eventually the ability to communicate breaks down. If it's okay to call a G-C#-E an A7, then is it also okay to call G-C# an A7?
If your answer to that question is yes, then my next question is: if it's okay to call a G-C#-E an A7 and it's okay to call a G-C# an A7, then isn't it also okay to call a C#, all by itself, an A7 too?
And if your answer is no because chords require 3 notes, my question is: why is the rule that chords require 3 notes more important than the rule that any variation of any A chord must have an A note present?
You don't actually have to answer those questions. I just wanted to point out why I think the practice of breaking the rules should be kept to a minimum.
You bring up good points, but I guess I just feel that the rules can be
bent much more than you can.
I mean, think about it: It would be silly and impractical if this type of thinking were put into practice.
Singer: Ok, let's take it from the A7.
Guitarist: Where?
Bassists: The A7, at the beginning of the verse.
Guitarist: Hmmm .... well ... I'm not playing A7 there. I'm playing C# diminished.
Bassist: Well, yeah .. you're playing only three notes, but I'm playing the root note, A, so the chord you're playing functions as an A7.
Guitarist: Well ... sure ... but this chord really can't be called an A7 if I'm not playing an A.
Singer: Shut up, both of you. Ok (to bassist), let's take if from the A7 ... (to guitarist) let's take it from the C# diminished.
I know this demonstration is a bit absurd, but I'm just trying to make a point. There are some "chords" that simply don't make sense if you force another root on them.
Case in point:
---10---
---10---
---9----
---9----
--------
--------
This chord could be called many different things: Bm11 would be one possibility. Or maybe E7sus4.
However, if you played this chord at the end of a jazzy tune in the key of G, it will sound like a G6/9 chord. In fact, it
is a very common 6/9 voicing.
It could also function as a D6/9 chord (in which case it actually would contain the root).
So, my question to you is this. Would it make sense in the music to call this an E7sus4 chord as the final chord to a song in G? (When the bass in fact plays G at the end too).
If your answer is no, then you agree that context
should play a role in the naming of a chord, and the "rules" of chord naming don't exist in a vacuum. They rely on context too.
This is really just more a matter of a philosophy than a matter of fact.