Thirds can be major, minor, augmented and diminished. Below you can see
that the number of half steps determines the quality of a third:
Major third, 2 whole steps or 4 half steps:
Minor third, 1 1/2 whole steps or 3 half steps:
Augmented third, 2 1/2 whole steps or 5 half steps:
Diminished third, 2 half steps:
A third can be identified by analyzing the seconds between the lower
and higher notes and a middle note inside the third. For example, the
third C-E has two seconds: C-D and D-E. Using the following table we can
find out the quality of the third:
|If the seconds are:
||then the third is:
|minor - minor
|major - minor
|major - major
|augmented - major
Following this method we find that the third C-E is a major
third because both seconds (C-D, D-E) are major seconds.
If any note has accidentals, we can determine the quality of the
interval without accidentals and then analyze the effect of the
- Make all notes natural. A-B is a major second, B-C
is a minor second, so A-C is a minor 3rd.
- Add a flat to A. The interval is now a major
- Add a flat to C. the interval is now a minor
Other ways of identifying thirds
- Associating thirds with scales, triads, etc. For example, the third D-F#
can be associated with the I and III degrees of the D Major
scale, or with the third of the D Major triad. If we know that
the third from the I to III degrees in major scales and the third of a
major chord are major, we know then that D-F# is also a major third.
- Memorizing all major and minor thirds. Start with major thirds and
continue with minor thirds. You will learn them with practice.
- Learning the number of steps for each type of third and counting the
whole and half steps (not recommended).