Triad

A triad in music is a special type of chord containing three notes.
These are the 1st, 3rd and 5th notes of a scale or key.
Or they can be thought of as three notes (1st, 3rd and 5th) on each note of a particular scale, they are different ways of looking at the same thing.
An example will make this clear:
- Here are all the triads in the key of C major:
- Here are the (root) triads of the keys of C, D, E, F, G, A and B major:
- Notice that, for example, the root triad in F major is the same as the traid on F in C major, similarly for G major
- The only anomoly is the last one of the first example, the notes B, D and F, which is not the root triad of any scale, so perhaps is not strictly a triad at all.
Triads form the basis of most Western harmony, certainly from the 16th to the 19th centuries