I am confused when people refer to a chord being built on a certain scale degree. For instance if someone says "this chord is used as a subdominant on such and such a degree of a scale" or "this chord acts as a tonic in the minor mode".

I understand what degrees of the major scale are and the numbering of each degree. So I presume that depending on the degrees used to build your progression the function of a chord may change. So a chord can change from being used to create a sense of expectation in one progression can alter to become a resolving chord in another?
Last edited by Fpink at Oct 29, 2016,
Don't think of chords in terms of letters when you study functional harmony. A "c"-chord can have a number of different functions depending on the key. C major in key of C major is the I-chord, or the tonic. So, it's the "home chord" that usually acts as the resolution to a chord progression, in other words it's the chord of least tension in a key. In the key of F major, the same chord (C major) would be the V-chord, or the dominant, that is traditionally the chord of greatest tension in a key that resolves to the tonic (this isn't technically true, as non-diatonic chords definitely have greater tension than the dominant).

A simplified explanation of chord functions in the key of G major for example would be something like this:

I - tonic. the home chord, G.
ii and IV - chords that often follow the tonic and lead into the dominant. IV is usually known as subdominant. Am and C.
V - the dominant. point of tension that resolves to the tonic. D.
iii and vi - embellishing chords with little tension. occasionally work as a substitute to the tonic, for example by preceding the subdominant. Bm and Em.
viio - a tense chord that works as a substitute of the dominant, but doesn't resolve quite as well traditionally. F# diminished.

You can apply these roles to any key and they work just the same. Usually you can't alter the chord function without changing the key, is that what you're after?
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So a chord can change from being used to create a sense of expectation in one progression can alter to become a resolving chord in another?

Yep. A chord's function comes from its relationship to the tonic and the other chords in the progression.

Scale degrees will always be based on the key. If you're in the key of Bb, that means Bb is the tonic, C is the supertonic, D is the mediant, etc. Those are the functional names for the chords, but it's also perfectly acceptable and probably more flexible to call them just "scale degree one/two/three" etc.

For a better understanding, I'd recommend just writing out the 12 major keys with note names going vertically, and then filling in the triads for each scale degree:

D major

Scale deg      Note    Rest of Triad
1                D        F# A
2                E        G  B
3                F#       A  C#
4                G        B  D
5                A        C# E
6                B        D  F#
7                C#       E  G

And there you'll have every key's diatonic triads, next to the scale degree.
Last edited by cdgraves at Oct 29, 2016,