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I probably described that poorly in the title, and I'm not even sure there is a word for what I'm thinking.

Lets say you're playing on just the white keys on a keyboard. C E G is C major, and D F A is D minor, the next chord after that. The number of steps between the notes in each chord is different, but they're the same number of notes within the scale apart.

Is there a word that describes the number of notes apart within a scale like that?

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2 Answers 2

up vote 14 down vote accepted

Sure is! These are called Intervals. It has to do with the number of "Scale Degrees" that separate two notes - basically, the number of notes you have to move through the scale from the first note to reach the second note (including the note you started on). These are worded "Second", "Third", "Fourth", "Fifth", "Sixth", "Seventh", "Octave" (Octave indicates an 8 note separation)

So, in your example:

  • C to E is a third (because you have to go from C (1) -> D (2) -> E (3))
  • E to G would also be a third (E -> F -> G)
  • C to G is a fifth (C -> D -> E -> F -> G)

You get a bit more complicated if you consider more unusual notes. For instance, C to Eb would be a minor third, because it's only three half steps. A more exhaustive list of Interval names is located here, but these are the basics.

I hope this helps. Disregard if I've misunderstood your question =)

EDIT: Just to be more clear / complete here (in case wikipedia ever disappears ;)):

Number of half steps    Interval Name
0                       Perfect unison
1                       Minor second
2                       Major second
3                       Minor third
4                       Major third
5                       Perfect fourth
6                       Diminished fifth, or augmented fourth
7                       Perfect fifth
8                       Minor sixth
9                       Major sixth
10                      Minor seventh
11                      Major seventh
12                      Perfect octave
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CEG and DFA both have the same interval then, despite being a major and a minor chord, is that correct? –  Alex Aug 25 '11 at 14:44
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I've updated the answer with a bit more detail, I should have included that in the first place! –  jadarnel27 Aug 25 '11 at 14:55
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E -> G is a minor third. A chord that spans a fifth (like all of the ones discussed so far) contains one minor third and one major third. In CEG the major is first; in DFA it's second. If you have two major thirds, your overall interval is a tritone, not a fifth. –  Monica Cellio Aug 25 '11 at 15:23
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@Monica +1 Good catch! I can't believe I actually typed that E -> G was a major third haha. –  jadarnel27 Aug 25 '11 at 15:27
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@Monica: A tritone consists of three tones, which would be about two minor thirds (except for comma's). Two major thirds amounts to an augmented fifth or a minor sixth. –  Raskolnikov Aug 25 '11 at 20:20

In addition to jadarnel27's excellent answer, I think it's worth discussing diatonic intervals. A diatonic internal is one that is composed entirely of notes in a scale.

For example, in the key of C, a C major chord is made of the notes C E G. The interval between C and E is a major this. A d minor chord is spelled D F A and has a minor third between the D and the F. However, in the key of C, both intervals can be described as diatonic thirds because they are thirds in the C major scale, even though they are of different qualities.

Hence, most typical chords in a typical scale or mode can be said to be made of a diatonic third and a diatonic fifth above the chord's root.

The word "diatonic" can be used to describe other musical ideas when you're only interested in the notes in a particular key. For example, let's say you have a motif in the key of C that you want to transpose to the key of A. You can do this by transposing up a major sixth, moving all notes the same number of semitones. However, this will lead to some notes outside of the C major scale. For instance, an E would be transposed to a C#.

You could also transpose by a diatonic sixth. In this case, all notes are moved up six scale degrees in the key of C. The precise interval each note is moved will vary as a result. C will be transposed a major sixth to A and E will be transposed a minor sixth to C, but they will all stay in the key of C.

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Here is a Wikipedia article about diatonic sounds: en.m.wikipedia.org/wiki/Diatonic_and_chromatic –  Kevin Nov 11 at 20:50

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