Years ago when I started to learn the basics of music theory I made the musical clock for myself by over-writing the numbers by the names of notes:
___________
/ C \
/ B O \
/ \
| O D |
| |
| A O O |
| |
| O E |
\ /
\ G F /
\_____O_____/
The o's are the black keys on the piano - e.g. o between C and D is C sharp (and D flat).
This clock can help you too - in several different ways:
1) Memorising the basic three chords in the key
These three chords (tonic, subdominant and dominant) form the "Y" shape on the clock: (example in the key of C)
___________
/ C \
/ B O \
/ | \
| O | D |
| | |
| A O O |
| / \ |
| O / \ E |
\ / \ /
\ G F /
\_____O_____/
By rotating the "Y" shape you are able to memorise the three basic chords in all other keys.
2) Transposing all chords
If there is a song in key G with the chords G Em C Am D (etc.) and you want to play the song in the key of D, move all chords 25 minutes backwards on the clock
3) Chords building
If you know that for example the major triad is made by the major third (= 20 minutes) and minor third (= 15 minutes), you are able to name the notes of every major triad (e.g. F#, +20 min => A#, +15 min => C#)
4) Chords recognising
When you see some group of notes, you can draw them (physically or in your mind) into the clock and if you know the shapes ("spiders") for the chords, you are able to recognise the chord.
Example: Which chord is made by the notes A, Eb, C, F ?
On the clock it looks this way:
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A -----O----- O |
| \ |
| O \ E |
\ \ /
\ G F /
\_____O_____/
And if you know that the shape "cross with one late" is the major seventh chord with the root on this "late" arm, you recognise the F7 chord.
5) chords simplifying
Let us stay by the F7 example. Which three-note chords you can use instead of the four-note major seventh? There are four possibilities:
Omit the root (and obtain the Am5-)
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A -----O----- O |
| |
| O E |
\ /
\ G F /
\_____O_____/
Omit the third (and obtain the Cm4sus)
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A O----- O |
| \ |
| O \ E |
\ \ /
\ G F /
\_____O_____/
Omit the fifth (and obtain the Eb2sus5-)
___________
/ C \
/ B O \
/ \
| O D |
| |
| A -----O----- O |
| \ |
| O \ E |
\ \ /
\ G F /
\_____O_____/
Finally, omit the seventh and obtain the F triad only
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A -----O O |
| \ |
| O \ E |
\ \ /
\ G F /
\_____O_____/
Actually I do not remember the strange chord names (Cm4sus, Eb2sus5-) but the shapes. I made the survey of the shapes of most used chords and memorised them.
The way of derivation of major and minor triads using the clock is easy. The major triad is built with the root, the tone major third higher (on clock 20min later), and the tone minor third higher (15min later). See how it looks on the clock: e.g. C major
___________
/ C \
/ B O \
/ | \
| O | D |
| | |
| A O_ O |
| / \_ |
| O / `- E |
\ / /
\ G F /
\_____O_____/
In the minor triad the intervals are switched: root, then minor third (15min), and then major third (20min). On the clock: e.g. A minor
___________
/ C \
/ B O \
/ | \
| O | D |
| | |
| A ---- O_ O |
| \_ |
| O `- E |
\ /
\ G F /
\_____O_____/
You should recognise that the examples shown above can be visually derived (by bending one arm 5min forwards or backwards) from the symmetrical "Mercedes" shape (which is actually the augmented triad):
___________
/ C \
/ B O \
/ | \
| O | D |
| | |
| A _0_ O |
| _/ \_ |
| O -' `- E |
\ /
\ G F /
\_____O_____/
In case of four tone chords the Cross shape (actually diminished seventh chord) works as the symmetrical base:
1) cross shape = dim 7th (here Cdim or Ebdim or F#dim or Adim)
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A -----O----- O |
| | |
| O | E |
\ | /
\ G | F /
\_____O_____/
2) bend one arm 5 min backwards and you receive major seventh chord rooted just on that bent arm (here F7)
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A -----O----- O |
| \ |
| O \ E |
\ \ /
\ G F /
\_____O_____/
3) bend one arm of Cross shape 5 min forwards and you receive half-diminished chord rooted on the arm to which the moved arm went closer (here Am75-). This chord is actually the ninth chord without root - the root is the note 10 minutes backward from moved arm (here F9, compare with previous F7)
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A -----O----- O |
| / |
| O / E |
\ / /
\ G F /
\_____O_____/
4) bend two neighbouring arms of Cross shape clockwise and you receive minor seventh chord rooted on the arm to which both arms went closer (here Am7)
___________
/ C \
/ B O \
/ | \
| O | D |
| | |
| A ---- O_ O |
| / \_ |
| O / `- E |
\ / /
\ G F /
\_____O_____/
Not enough?
OK - here are all ten existing shapes of four-note chords without halftone (5min) distance.
Cdim (C, Eb, Gb, A, actually C, Eb, Gb, Bbb)
___________
/ C \
/ B | O \
/ | \
| O | D |
| | |
| A -----O----- O |
| | |
| O | E |
\ | /
\ G | F /
\_____O_____/
Cm75- (C, Eb, Gb, Bb)
___________
/ C \
/ B | O \
/ | \
| O -._ | D |
| \_| |
| A O----- O |
| | |
| O | E |
\ | /
\ G | F /
\_____O_____/
C75- (C, E, Gb, Bb) Do you see the symmetry? It is also F#75-
___________
/ C \
/ B | O \
/ | \
| O -._ | D |
| \_| |
| A O_ O |
| | \_ |
| O | `- E |
\ | /
\ G | F /
\_____O_____/
C7 (C, E, G, Bb)
___________
/ C \
/ B | O \
/ | \
| O -._ | D |
| \_| |
| A O_ O |
| / \_ |
| O / `- E |
\ / /
\ G F /
\_____O_____/
C74sus (C, F, G ,Bb)
___________
/ C \
/ B | O \
/ | \
| O -._ | D |
| \_| |
| A O O |
| / \ |
| O / \ E |
\ / \ /
\ G F /
\_____O_____/
Cm7 (C, Eb, G, Bb)
___________
/ C \
/ B | O \
/ | \
| O -._ | D |
| \_| |
| A O----- O |
| / |
| O / E |
\ / /
\ G F /
\_____O_____/
Cadd9 (C, E, G, D)
___________
/ C \
/ B | O \
/ | \
| O | _.- D |
| |_/ |
| A O_ O |
| / \_ |
| O / `- E |
\ / /
\ G F /
\_____O_____/
C75+ (C, E, G#, Bb)
___________
/ C \
/ B | O \
/ | \
| O -._ | D |
| \_| |
| A _O_ O |
| _/ \_ |
| O -' `- E |
\ /
\ G F /
\_____O_____/
C6add9 w/out 5 (C, E, G, A, D), it is D9 w/out 3 (D, F#, A, C, E)
___________
/ C \
/ B | O \
/ | \
| O | _.- D |
| |_/ |
| A ---- O_ O |
| \_ |
| O `- E |
\ /
\ G F /
\_____O_____/
C9 w/out 5 (C, E, G, Bb, D)
___________
/ C \
/ B | O \
/ | \
| O -._ | _.- D |
| \_|_/ |
| A O_ O |
| \_ |
| O `- E |
\ /
\ G F /
\_____O_____/
From the four note chords with halftone I will draw C7maj only - the rest (Cm7maj etc) is your homework :-)
C7maj (C, E, G ,B)
___________
/ C \
/ B O \
/ \ | \
| O \ | D |
| \| |
| A O_ O |
| / \_ |
| O / `- E |
\ / /
\ G F /
\_____O_____/