When playing the guitar, how do I know which scale to play over a chord progression?

Answer 1

Hey Bryce,

In some of your comments you gave a hypothetical chord progression of "Am, F, C, G." It's a bit easier to form a response with this information.

The answer can actually be quite long, BUT we can approach it from several directions:

The "Correct" Way

This will require you to have a low-intermediate grasp of music theory. You will want to understand the formula for your diatonic scale, which is the basis of all this western music theory we tend to use. You will need to be able to name just about any note on your fretboard. You will need to know the formulas or at least the chord shapes for the chords you mentioned. (Am, F, C, G.)

Knowing your circle of fifths and key signatures would help, but is not necessary.

What you will then want to do is write down all the notes that show up in your chord progression, removing any doubles. For instance, the Am chord consists of: A, C, E. The F major is: F, C, A. etc.

We should hopefully end up with seven notes. Any less and the exact "key" of the piece becomes a bit harder to pin down. You might have to look at more than just the notes comprising the chord progression to discern the key.

In our case, for the chords given, we have 7: A, B, C, D, E, F, G. With this information, most musicians who read music or who have received some more "traditional" instruction would simply look at the number of accidentals (sharps or flats), and know right away that this piece is in C major (no accidentals), which is enharmonic with A minor. In that case, you could use any scale which is derived from C major (like A minor pentatonic) over this progression.

If any of that went over your head, that's okay. You don't have to go the "correct" route, you can also go:

The "Incorrect" Way

If you been approaching music from an "intuitive," "self-taught" perspective, this might be easier, especially with pentatonics. Now, it doesn't work with everything, and you'll continually have to develop your ear and intuition to be able to apply this sort of "internal" method to new and more complicated types of music, but since the chord progression you gave is simple, you can go about it this way:

1) Find the root note of the piece. It's usually the root note of one of the chords, most likely the first chord in the song. (Am) You'll know it's the root note because if you just keep picking it over and over again for a minute or so straight, it'll still sound good with pretty much all of the chords. So with your chord progression: Am, F, C, G, try playing an A note, an F note, a C note, and a G note over and over again. Find the one that sounds the most "consonant," (good, strongest, most like "home"), for the most part of the song, and that is most likely your root note.

2) Find your 3rd. Once you have your root note, check to see if the next good-sounding note is a major 3rd(4 frets up), or a minor 3rd (3 frets up).

From the note you've decided is the root note, try to play a note 4 frets higher. If it sounds good, your piece is major.

If it doesn't sound good, try to play a note 3 frets up instead. If that one sounds more correct, your piece is minor.

3) You're off! If you discerned the piece was major, use your major pentatonic. If you felt is was minor, use your minor pentatonic. Pretty easy.

This whole process can be performed entirely by ear, without even knowing the chord progression. Once you've internalized and become familiar with what a root note "feels like." You'll be able to find it on the fretboard even if you're not familiar with the piece, from there you can try step 2, figure out if it's a major or minor key, and you're off.

This is most reliable with pentatonics, though. It takes a bit more doing to move into diatonics this way, although the process is essentially the same.

The "Ideal" Way

Learn both. There are benefits to being able to process musical information in multiple ways. Only being able to play from a mental/"correct" or intuitive/"incorrect" space makes you an incomplete musician in either case. Having a good ear and capacity to express oneself in music is just as important as understanding the theory.

Answer 2

Answer 3

A chord progression is determined by the key (scale), not the way you ask.

It is also determined by the mode - major or minor.

Also the purpose of the progression. Is it to modulate. Is it to give a cadence?