How to Harmonize the Major Scale to Build Triads and Chords on the Guitar
A triad is a set of three notes stacked in 3rds. Playing in 3rds on the guitar means that you start on a scale degree, count it as 1, and then move to the scale degree that is three away, 3. For example, the G major scale is G-A-B-C-D-E-F♯.
If you start counting from G, then the 3rd is B (G-A-B, 1-2-3). If you start counting from A, then the 3rd is C (A-B-C, 1-2-3).
A triad is three notes that are all a 3rd apart. For example, in the G major scale, G and B are a 3rd apart and B and D are a 3rd apart. Together all three of these notes are a 3rd apart, called two consecutive 3rds. G-B-D make a G triad.
You also call the members of the triad root, 3rd, and 5th because counting from the starting point, G, B is the 3rd degree and D is the 5th.
G A B C D E F♯
1 2 3 4 5 6 7
G B D
1 3 5
Harmonizing a root, 3rd, and 5th together (in other words, playing them simultaneously) produces a chord. Basically, the difference between any old chord and a triad is that a chord is a group of three or more notes, and a triad is specifically a root, 3rd, and 5th.
You build triads on all scale degrees by following a formula of 3rds. Not all triads are the same. Because of the half step and whole step formula of the major scale, some 3rds are closer or farther apart than others. As a result, there are major triads and minor triads. One triad is diminished.
Major triad: Building from the 1st scale degree of the major scale
Building a triad starting from the 1st degree of the major scale produces a major triad. Sounding the triad’s notes produces a major chord. In the first diagram, you see all 7 degrees of the G major scale in one sample position. In the second diagram, you see just the root, 3rd, and 5th triad. When you strum all three of these triad notes simultaneously, you play a chord.
Specifically, this chord is G major — G because the root is G and major because the distance between the root and 3rd is two whole steps, which make up a major 3rd. The third diagram shows you that the actual note names of the G triad are G, B, and D.
A G major chord is always made from the notes G-B-D; however, you can have more than one occurrence of each note. For example, you can play a G major chord as G-B-D-G or G-B-D-G-B. You can even stack the notes out of order like this: G-D-G-B.
Whatever order you play the notes in and however many occurrences of each note you play, all combinations of G-B-D produce harmony that’s recognized as a G major chord.
Notice that these common G major chord shapes all use the same notes, although not necessarily in the same number or order. Chords like the ones shown here are considered triads because, technically, they’re still based on three pitches even though they vary in the exact number and order of their notes.
Minor triad: Building from the 2nd scale degree of the major scale
Using the G major scale, count one-two-three-four-five from the 2nd degree, A (A-B-C-D-E), and take every other note, 1-3-5 or A-C-E. This is an A minor triad — A because the root is A and minor because the distance from 1 to 3 is a step and a half, which makes up a minor 3rd or flat 3rd (♭ó3) interval.
Check out how to build a triad from the 2nd major scale degree, A. The major scale used here is exactly the same as the one used for the previous triad, G major.
The only difference is that you’re now counting from the 2nd scale degree, A, to determine its 3rd and 5th. The G note was left at the 3rd fret of the 6th string blank so that you know not to start on it.
You can play the note A either on the open 5th string or at the 5fth fret of the 6th string. You need to do the latter to play the triad as a chord. You can see that the notes of this A minor triad are A-C-E.
Notice that these common A minor chord shapes all use the same notes, although not necessarily in the same number or order. (In case you don’t know, an X at the top of a string indicates that you don’t play that string.)