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My question deals with what scale to play over a given chord progression.

For example, consider a progression containing I,II,IV,V in C. I.e., the rhythm guitar is playing C, Dmin, F, and G...

My intuition tells me that if I am going to improvise over these chords, I would stay in the C-scale the entire time, because, indeed each of these chords are on the C-scale.

However, I've been told that I could indeed play in C while the rhythm guitar is playing Cmaj, in F while the rhythm guitar is playing Fmaj, etc.

But again my intuition tells me that I would then be playing out of key.

Which approach is correct, or are both? Is there a general rule? Does it depend on the genre of music? (I'm playing bluegrass)

Thanks

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5 Answers 5

up vote 10 down vote accepted

By staying in the scale of C maj., most notes will work over most chords made from the diatonic C scale.Even an F note over a C chord can be made to sound fine,so yes, stick with C scale notes. Some may sound inappropriate, depending where in the bar they appear.

However, taking the second idea, think about, for example, F scale notes - only the Bb is different.The Dm scale- again only Bb. The G scale - only F#. So, you can see that when following the chord changes using the new scale notes, at any given bar, there's (usually) only one note from the 'new key' that will maybe clash.Having said that, the 'odd' note sometimes works really well, to give an extra colouring to the solo/tune.

It will also depend where you've come from and where you're going. E.g. on C, going to an F bar, the Bb comes nicely into its own, signalling a C7 sound that usually leads to F anyway.

If you approach it modally,then for each chord you will have the same choice of notes - C maj. scale. The difference can be that you'll centre ,for example , on D for D dorian, etc, but that's what happens anyway.

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I think the problem is in keys and modulation. If you stay in C, you can make most notes of the scale work over the progression - trust your ears about what sounds right. If you switch keys for each chord, what you're saying is the music has modulated to that key (very quickly); and without any real preparation and resolution it will sound quite jarring (google 'truck driver's gear change'). –  Faelkle Jul 18 '13 at 8:30
    
I am not saying the music has modulated quickly, only that the selection of notes has varied in a small way. If one only knows one scale position, then changing to a new position is a non-starter. If one knows that , say, the scale notes for C maj. change by one note when moving to G maj., then the same fret/string places will still be used, with only a change from , in this case, F to F#. And this F# possibly/probably won't be used anyway.If one is au fait with modes, one could think in terms of 'now I'm not in C maj., but C Lydian over a G bar'. –  Tim Jul 18 '13 at 9:56

You can approach it with the single scale (C) and think of certain notes as "avoid notes". For instance, while playing on a Cmaj you would avoid F. This is because it clashes harmonically with the notes in the chord. You can still play F but it usually feels like it isn't part of harmony and needs to resolve to something that is, which would usually be E in this case. The avoid notes would be different when the chords change though. This "avoid note" concept is based on a Jazz thought process in which notes are deemed avoid notes by being a half-step above a chord tone (F is a half-step above E and E is a chord tone of Cmaj). Other answers have suggested you use your ears, which I agree with, and if you notice which notes don't sound good or need to be treated more delicately and when/over which chords they occur, you will be hearing the avoid notes.

You will also find that notes that are a half-step below chord tones can be dissonant in the same way but aren't referred to as avoid notes. This has to do with chord voicing, for example on a Cmaj7 you wouldn't want to play the root (C) above the 7 (B) because it would create a harsh dissonance different than the intended chord, ie what the chord symbol means.

The Jazz approach would suggest that you would play a scale for each chord, known as chord-scale theory. If you want to stay completely in the key then you are just playing each mode (Ionian-Dorian-Lydian-Mixolydian in your example). Most Bluegrass will have a good amount of "Blue Notes", which can occur in different places but often include playing b3 or b7 on a major chord or #4/b5 on a minor chord.

Traditional Jazz is often taught with the concept that each chord-scale would have more to do with the type of chord than the key you are in. Scales with no avoid notes (Dorian and Lydian) are used in place of the expected modes unless they are Dominant or Diminished chords. For example, the chord-scale for I in a major key would be Lydian or Dorian in minor.

The chord-scale approach could work well for you but you probably won't be playing Lydian and Dorian quite as much as the Jazz guys. You will likely be playing more blues scales, where you could turn every major chord into a dominant 7, and a lot more of the other modes.

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You generally want to identify the tonal center of the song (or section of song) and use an appropriate scale that establishes that center. The chords you give are those that fall into the subdominant, dominant and tonic chords in the key of C - the chords themselves help to establish the key.

But forget about the word "scale" - you don't want to be thinking of "scale" for improvisation - you rather need to think of target tones - of course in many cases these are derived from a scale, but at any given point there are only a subset of tones that are appropriate - giving equal weight to all tones in the scale is not the right thing to do.

Each chord has a set of valid chord tones + tensions, and also a set of tones that clash and are to be avoided. See the Wikipedia page on "avoid notes:" avoid notes

For more details, see Understanding and Implementing Harmony

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The chord progression you stated, I,II,IV,V, is very common in popular music, and you also let us know that you are playing this in the key of C major. As C is the tonic or root note in this key it would be most logical to play a melody in a C Major scale. Even though your rhythm guitar is playing other chords, all the chords you stated belong to the C major scale.

Yes, you can play other scales or modes as suggested by Chochos that's plenty ok, and you should allow yourself the freedom to explore this avenue. But the basic question is can you play a C major scale while your rhythm guitar is playing a F major chord, and the answer is yes, because F major is the subdominant chord for the key of C major.

Recall that in a major scale I = the tonic (in the Key of C that would be a C major chord), while you have II for the super tonic, in a major key this is minor and it should be written as ii.

The entire chord scheme for a major scale is as follows: I – ii – iii – IV – V – vi – vii°

(major, minor, minor, major, major, minor, diminished)

Names: tonic, supertonic, mediant, subdominant, dominant, submediant, leading tone

The important thing to understand here is that melodies are relative to the key signature for tonal music. Tonal music defines a tonal center, in this case, C. If you listen to Bach or Handel's music you will find shifts in key centers, these are called modulations, and this only means that the music 'modulates' from one key to another and so does the harmonic and melodic structure shift to a new key center.

Additionally, since you mention you are playing Bluegrass, consider that this idiom allows for many alterations to scale as in bending notes per fiddle, guitar, or banjo. For instance in Blues the 3rd scale degree is often played both minor and major in the same measure.

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You could use modes; that is, play the Ionian scale in C, then Dorian when the chord is Dm, play Lydian on F and Mixolydian on G. That way you stay in the key of C, but you're moving the emphasis to the root of each chord, or you could put the emphasis on the color notes of each mode.

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