D Suspended 4th
sus4
0 - 5 - 7Root + perfect 4th + perfect 5th
About D Suspended 4th
Dsus4 is the D triangle with one extra finger — and it is probably the most-played suspension on the guitar. The G replacing the F♯ sits at the third fret of the high E string, exactly where the little finger already hovers, so the figure D–Dsus4–D costs nothing to play and appears everywhere.
The notes
D, G, A. No third, so the chord has no mode; but the fourth leans hard, and the ear expects it to fall back to F♯.
That expectation is why the chord almost never stands alone. It is a gesture rather than a harmony — a delay before the arrival of plain D.
How it is used
Alternating with D on the beat, usually with the little finger adding and releasing the G while the rest of the hand stays put. The figure is so common in folk and rock that many players do it unconsciously.
Held longer, it works as a substitute for the dominant in modal writing, where the missing third keeps the harmony open and the fourth supplies the motion.
Where it shows up
In the key of D as an ornament of the tonic, and in the key of A as a suspended IV. It also appears at the end of a phrase where the resolution to D is deliberately delayed by a bar.
Together with Dsus2 it gives three chords from one hand position, which is why so much acoustic writing in D moves between them without ever leaving the shape.
Guitarists also use it to disguise a change of hand position: holding the suspension for a beat gives the fingers time to move, and the listener hears an ornament rather than a hesitation.