Originally Posted by: Lao_Tzuhi everyone I have just worked out the modal approach to things but I would like to understand where sus chords fit in because they are neither major or minor since the 3rd is replaced by either the p4 or m2. i was wondering where they fit in, inside the major scale chord sequence. and how do you use the sus notes to highlight what mode you are in. this is what i want to understand. where to use sus chords, why use them, and when to use them.

this chart identifies the possibilities of chords in major scales

https://kingofchordsblog.files.wordpress.com/2016/02/chord-possibilities-in-major-keys.pdf

the first chord of A Major key could become,

A major 1 3 5, Amaj7 1 3 5 7, Amaj9 1 3 5 7 9, Amaj13 1 3 5 7 9 13, A6 1 5 3 6,

Aadd9 1 3 5 9 , A6/9 1 3 5 6 9, Amaj7/6 1 3 5 7 6 , Asus2 1 2 5 , Asus4 1 4 5.

There's an Asus2 in there. So a possibly variation could be to replace an Amaj9 with Asus2

example in a song

Message in a Bottle, The Police.

C#sus2 Asus2 Bsus2 F#m add9

chords from the key of C# MInor/E Major

C#sus2 is I in C#Major, II in B, IV in G#, V in F#, VI in E

Asus2 is I in A, II in G, IV in E, V in D, VI in C

Bsus2 is I in B, II in A, IV in F#, V in E, VI in D

F#m add9 is II in E, III in D, VI in A

Common denominator.......E Major

The ear likes the mystery of sus2s and sus4s.