The Mudcat Café TM
Thread #125950 Message #2794186
Posted By: Piers Plowman
22-Dec-09 - 06:47 AM
Thread Name: The three chord trick
Subject: RE: The three chord trick
Subject: RE: The three chord trick
From: Pip Radish - PM
Date: 22 Dec 09 - 05:21 AM
"Piers - that looked fascinating but I didn't get very much of it; you seem to have started with Lesson Four!"
Sorry, I'll try to explain better.
From your original posting:
"This leaves me with a puzzle: it suggests that the 1, 4 and 5 chords, plus their relative minors, are the only chords which are possible in any given key signature. I assume this isn't the case, or the whole of Western music would sound like Status Quo."
Well, actually it sort of is the case, except that there is the additional diminished triad, if we just take the triads.
Triads in C:
C E G --- C maj.
D F A --- D min
E G B --- E min
F A C --- F maj
G B D --- G maj.
A C E --- A min.
B D F --- B dim (without the seventh)
It gets more interesting when we take the seventh chords:
C E G B --- C maj. 7
D F A C --- D min 7
E G B D --- E min 7
F A C E --- F maj 7
G B D F --- G dom. 7
A C E G --- A min 7
B D F A --- B half-diminished seventh
These are indeed the only seventh chords possible if you remain strictly in the key of C. Lots of songs do remain in a single key for their entire duration, especially children's songs, Christmas carols and folksongs, although even this is an over-simplification.
As you've noticed, there is a relationship between the chords with the minor thirds and the ones with the major thirds. This becomes even more clear when you look at the seventh chords. The D min7 chord contains the F maj. triad, the E min 7 contains the G major triad and the A min 7 contains the C maj. triad. This is useful for substitutions, i.e., one can often play a Dm7 instead of an F maj. chord.
Many songs don't just stay in one key. One uses altered tones or alterations to make things more interesting and there are a number of standard ways of doing this. One common way is to "modulate" into another key, briefly or for a longer period of time. What I wrote in my last posting was an explanation of one way of modulating.