Consonance And Dissonance In Music

Consonance And Dissonance In Music

This article is useful in the practice of improvisation. It will explain why certain scales can be used to good effect in improvising and also why a certain amount of chord theory is handy.

If you don’t understand what the term interval means, you should first go and read over the following post; Intervals And Their Qualities. 

Major and perfect intervals in a C major scale

So, having established what an ‘interval’ is, we can move on to the concept of consonance and dissonance.

It’s a rather simple concept that states that certain intervals harmonize or are pleasing to the ear and certain intervals clash or are unpleasant to the ear. Naturally this is a bit subjective and changes somewhat from era to era, but we can establish a basic overall accepted norm and work from there.

The intervals, which harmonize and are known as consonant, are specifically the thirds and sixths, regardless of their quality (major or minor.) Fourths and fifths are also considered consonant but with a somewhat less harmonious quality than the thirds and sixths. The exception is the diminished fifth which is considered dissonant and has historically been called ‘The Devil’s Interval,’ but that’s another story. The eighth or octave is also considered consonant.

The dissonant intervals are the seconds and the sevenths in whatever quality. 

Now, how does this information fit in with improvisation? Well, there is a relationship between the chord progression and the melody. Ideally the melody should be made up of mostly intervals, which are consonant with the chord. It is not, strictly speaking, necessarily desirable to have all note in the melody be consonant with the chords as a good mix of consonant and dissonant intervals will give the music some interest and edge.

It is chiefly desirable that the consonant intervals fall on the beat. Dissonant intervals work best after the beat and resolving to a consonant interval.

Let’s take up an example. Suppose you have a C major chord. 

C Major Chord

This chord has the notes C, E and G in it. If you play a C major scale over this, you will have the notes C,D,E,F,G,A,B,C. 

C Major Scale

Obviously the notes from the scale C,E and G will be consonant. The notes D and A will be dissonant as they will be seconds to the notes around them but they will be major seconds and, if used in between two consonant notes, will not present much problem. On the other hand the notes F and B will give you minor seconds (B to C and F to E,) and minor seconds are the most dissonant intervals of all. You would be instantly in the realm of modern music.

This is why using other forms of scales can make improvising easier. The major pentatonic scale, for example, simply removes the forth and seventh notes of the major scale. In the case of C major, the F and the B would be removed, solving the problem of running into the minor seconds.