Intervals, Scales & Chord Spelling for Guitar

0. Introduction. 'Interval' means the musical distance (pitch difference)
between two notes. Scales and Chords can be related by the intervals they 
contain. Measurement of intervals is relative to the 'Major Scale'.

1. Chords named with a note only (C, G, D, etc) are the 'Major Chords'. 
They can be formed from the 1st, 3rd and 5th notes of their major scale.
In 4, 5 & 6 string 'voicings', one or all notes are doubled.

1.1 Rock '5' chords for guitar ('powerchords') played with just two notes 
omit the 3rd of the chord. With three string voicings the 1st is doubled.

2. 'Minor Chords' (Dm, Am, Em etc) are spelled 1st, b3rd and 5 of the MAJOR
scale starting on that note. The flat 3rd is not necessarily going to be a 
flat note. 

	Example Am - A scale: A B C# D E F# G#
			      1 2 3  4 5 6  7

			1=A	b3=C	5=E  

	This chord is usually played open over 5 strings
	A-E-A-C-E so A & E are doubled, and the b3 is C.

3. 'Dominant Chords' have either 7,9,11 or 13 after the letter part
(Ab7, Eb9, Bb11 etc) These chords are spelled 1 3 5 b7 (9) (11) (13) from
a MAJOR scale starting on the name of the chord.
	
	Example E9 - E scale: E F# G# A B C# D# E F# G# A B C#
			      1    3    5    7    9     11  13

			1=E	3=G#	5=B  b7=D  9=F#

	This chord is usually played over 4 strings as E-G#-D-F# so the 5th 
	is omitted.

3.1 Other chords with numbers in their names are 'add' chords and 'sus'
chords, generally 'add' means an extra note, whereas 'sus' means that 
the third is replaced. 'Sus' without a number means 'suspended 4'.

	Ex. i) 	Csus9 is spelled C-D-G. The 3, E, is replaced by D, 
		the 9 or 2. The name Csus2 (or just C2) is more correct,
		as 9 suggests that the seventh should also be present.

		Try the useful 3rd fret bar chord: C-G-C-D-G

	   ii) 	Cadd9 is spelled C-E-D-G
	        This is usually played as an open chord: C-E-G-D-E