Triads are the basis of all western music and are indispensable to the aspiring musician regardless of style or musical preference. Every time you play a C, G, A, Am, D, E, Em etc chord on a guitar you are playing a triad.
A triad is so called because it consists of 3 notes. The 1st, the 3rd and the 5th notes of the major scale.
We could use any of the major scales, but let’s take C major first since it has no sharps or flats:
C D E F G A B C
So the C major triad consists of C, E, and G
And everytime you play a C chord on the guitar you are only playing these three notes, from bottom to top you’re playing
String – Note
If we take the D major scale:
D E F# G A B C# D
We can see that the D major triad consists of D, F#, and A.
To take another example; A major, we would have:
A B C# D E F# G# A
A major triad = A, C#, and E.
So remember, a Major Triad is the 1st, 3rd, and 5th of the major scale