Theory

[paul_c2]

I just counted the major keys (the natural minor is a mode of the related major).

C major (no sharps or flats)
1-7 sharps
1-7 flats

Out of the 15 there's some which are enharmonic equivalents (Db and C#; Gb and F#; Cb and B)

[wateroftyne]

9 hours ago, jrixn1 said:

In language you have letters, which are the building blocks of words.  Then a level up, words are the building blocks of sentences.  Analogously in music, if notes are letters, and chords are words, then the circle of fifths is a very commonly-seen sentence.

Suppose you're handed a 32-bar chart in the key of Fm, and the final eight is:

If you're reading each chord in isolation, it might seem like an onslaught of unconnected chords, which gets quite fast-moving particularly in the final line - looks like some sharps and flats mixed in together, what's an F# and B doing there if we are in they key of Fm, why is there a B major immediately followed by a B minor, etc?

But if you can "see" the circles of fifths, you can more quickly make sense of what's going on at a higher level:

• an extended turnaround in the key of Ab (bars 25-28)
• a 2-5-1 in the key of B (bar 29)
• a 2-5-1 in the key of A (bar 30)
• a 2-5-1 in the key of Ab (bars 31-32)

When I say extended turnaround, I mean 2-5 3-6 2-5-1.  That and the simpler 2-5-1 are straight out of the circle of fifths.

So what's the point?  The advantage is that I'm very familiar with turnarounds; and now that I understand that this section is literally just turnarounds, I can use my usual grooves, fills, licks, substitutions, party pieces, whatever, and I know they'll fit musically, and I'll end up in the right place.

You'll encounter the circle of fifths more in jazz or jazz-derived music, and knowing what is going on musically is more useful if you're improvising or have the freedom/desire to vary your part, rather than playing a written or fixed repeated riff.  It could be that you just want to add a passing note between the Eb7 and Cm, and knowing whether it should be D or Db.  The chart above is 'Street Life', https://www.youtube.com/watch?v=cnNyxy7XPfs , 1m07s to 1m23s under the verse, and then again in the solos at 3m10s to 3m27s.

Thank you - that's very comprehensive.

I'm rarely (never?) in situations where I needs to improvise over tricky progressions, so I'm probably just not the target audience.