Guitar: The major cadence - The great triumvirate: An Open Learning Guide
You have now learned three chords: D, A and G major. Believe it or not, you can accompany hundreds of songs with just these three chords. Many songs are played with just three major chords.

You have now learned three chords: D, A and G major. Believe it or not, you can accompany hundreds of songs with just these three chords.
Many songs are played with just three major chords. The order of the chords can vary quite a bit, but within a key it is always the same three chords that you find together. Other major chords are rare in the key of D major and are then considered an exception.
Play the chord progression D G A D in exactly this order! This series of chord is called a D major cadence. A cadence is something like a standard chord progression that leads back to the basic chord. The D major cadence is used both for descriptions in harmony theory and for pure exercises of chords in the key of D major. It is something like a formula that represents all songs in D major that are only accompanied by the three chords D, G and A.
As soon as you get to know several songs, you will probably find out for yourself which major chords usually appear together and which major chords are rarely or almost never found together. In the circle of fifths, which you will get to know better sooner or later, the major chords that are often found together are arranged nicely next to each other as neighbors, as shown in the diagram above.
A few more minor chords are added later, but even then the triumvirate of the major cadence is usually retained.
Of course there are a few exceptions, but most of the songs we know in Western Europe stick to this simple division into a group of three.
is the root chord and also indicates the key of the entire piece of music. Unfortunately, you can't rely on it 100%, but a piece usually begins and ends with this basic chord.
As a mnemonic, remember: "The tonica indicates the ton."; and that a song should at least end with the tonic.
Of the three chords you have learned so far, the tonic is always D major. So always start and end your dry runs with D major.
The basic chord is almost always a kind of calming influence in the piece of music. How you change in between doesn't really matter. The main thing is that you come back to the basic chord D major.
Source and licence
Text adapted from Guitar/The major cadence - The great triumvirate by Wikibooks contributors under CC BY-SA 4.0. Paragraphs have been selected and abridged, and formatting adjusted. This adapted text is shared under the same licence. Contributor history.

