Quote:
Originally Posted by mr. beaumont
The 7th chord thing seems to be messing you up.
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I agree with most of your explanation, but I would offer one clarification:
A
SevenTH chord is a chord that includes the 7th degree of the chord build on that note:
D7 = D-F#-A-C
I think the theory to explain all of that has been covered very well by the posts so far.
A
Seven chord is the chord build on the seventh scale degree of the key in question:
In the key of G, F# is the seventh scale degree, so the chord built on top is the Seven chord. Seven chord is the general name: Diminished seven is the specific descriptor. F#dim is the seven chord in the key of G.
In parlance: Seven chord =/= Seventh chord.
This important distinction might be contributing to the confusion.
The reason for the -th is because we shorten the full name to a shorter name that retains all of the meaning: "A D Seventh chord" is just a shorter way to indicate that you should include the C, rather than just playing the basic D-F#-A triad. The C isn't always invited.
Cue the people who reverse these two terms in their mind: Music is a language. People use it in all sorts of ways to be able to communicate.