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Intervals

August 24, 2011

The distance between two notes is called an interval. 

The different intervals are called by numerical names: unison, second, third, fourth, fifth, sixth, seventh, and octave (ninth, tenth, etc.)  These tell how far apart the notes are on the staff.  Thus from a note on a line to the note on the next space: a second, from a note on a line to a note on the next line: a third, etc.

However, as we know from the major scale, do-re-mi-fa-sol-la-ti-do, not all seconds are equal.  Some are whole steps, and some are half steps, as shown below:

Thus there needs to be another descriptor for full precision.   To this end, intervals can be further designated as Major, minor, perfect, augmented or diminished.  Here is an easy way to remember which are which:  The intervals of the ascending major scale are either Major or perfect.  The intervals of a descending major scale are either minor or perfect.  (The perfect are the ones that are the same size in both scales.) Thus:

If unisons, fourths, fifths, or octaves are larger or smaller than their perfect size, they are called augmented or diminished.  For the other intervals, these names are applied if they are larger than their major form or smaller than their minor form.  The only augmented or diminished interval occuring naturally among the notes of the major scale has its own name: the Tritone (so called because it spans three whole steps).  If you spell it F-B, it is an augmented fourth, and if you spell it B-F it is an diminished fifth.  Try writing these out, and you will see why.  

The understanding of intervals is neccessary to many aspects of music.  If you understand the subject of intervals, you can begin to try your hand at counterpoint, which is the writing of one melody to be played simultaneously with another melody.  Different styles of counterpoint have different rules concerning the intervals used, and how they may progress from one to another, etc.  Intervals are also the basis of chords, and necessary to the study of harmony.  And of course, knowledge of intervals can be helpful when learning to read melodies.

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