Progressions are streams of changing chords. As we have seen, they are written as chord symbols, typically above something [rhythm notation, melody, lyrics]. Our goal is to continually expand our chord catalog. We do this by using chord learning systems, a simple sheet of chords, or just songs that we like.
To play a song, we look at all of the chords in the song [its chord inventory], determine which we know and don’t know. If we don’t know a chord, we find a version of it. If we don’t know an open string version [Chord Connect], we can use a R5 chord. By doing this, the song may not sound right, but is possible to play. Once we know all of the chords which need to be connected and have working versions, we go back and forth between each chord pair, until we know we have it. This way, when every chord change in a song is solid, the song will not break.
Number of Chords in a Song
One chord songs do exist. Many of them are used as rounds [songs with multiple singers singing the melody at different starting times – Row Your Boat, Are You Sleeping?]. There are also many two chord songs. Most often, simple songs have 3 or 4 chords, sometimes more.
Number of Progressions in a Song
Some songs only have one progression over and over. Yet, most songs are made of 2 or more progressions. 3 is very common. Some parts of songs are also riff-based, rather than chords being strummed [but there is always harmony implied].
Progressions build parts of songs. Song parts build whole songs. This structure of a song, in music, is called its form or song form.