May I ask the knowledge of music theory: what are the first chord, the fourth chord and the fifth chord respectively?

In tradition and acoustics, these three chords refer to T /S /D, which are the three most stable chords in the mode system. T is also called "main chord", S is called subordinate chord, and D belongs to chord.

Taking C major as an example, t/s/D is C chord, F chord and G chord respectively, and taking A minor as an example, T/S/D is am chord, dm chord and E chord respectively.

The chord types of T/S/D chords are different in different modes, but in general, the main chord consists of modes 1, 3,5, the subordinate chord consists of modes 4,6, 1, and the subordinate chord consists of modes 5,7,2.

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