“Finally, there are two types of triad that do not include a 3rd. These chords are normally named ‘suspended’ (or just ‘sus’ chords), as the lack of the 3rd gives an unresolved feel to their character. In a ‘sus’ 2 chord the 3rd is replaced with the 2nd of the scale, and in a sus4 chord, the 3rd is replaced with the 4th of the scale. In C, the notes generated by the formula 1 2 5 are C D and G Example 1g The notes generated by the formula 1 4 5 are C F and G. Example 1h ””
Guitar Chords in Context: The Practical Guide to Chord Theory and Application
