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To count an interval's degree, do exactly one thing: count from the lower note up to the higher one and see how many letter names are involved. C to E is C, D, E — three names, so a third. C to G is C, D, E, F, G — five names, so a fifth.
That is all there is to it, yet beginners get it wrong almost every time, for one reason: they are still thinking in semitones.
Count names, not keys
| Interval | Letter names counted | Degree |
|---|---|---|
| C to D | C, D | second |
| C to E | C, D, E | third |
| C to G | C, D, E, F, G | fifth |
| C to C (an octave up) | C, D, E, F, G, A, B, C | octave |
Degree looks only at letter names and has nothing to do with how many black or white keys lie in between. The first counter-intuitive consequence: one degree can come in different widths. C to E spans four semitones; D to F spans three — both are thirds, because both contain three letter names.
That difference in width is not an exception but the norm. It is decided by semitones and whole tones, and it is why major and minor intervals exist at all.
A rule of thumb: count both endpoints
Counting only the notes "in between" is the classic mistake. C to E has just one D in the middle, but it is a third, not a second, because C and E count too. The eight degree names are really just "how many letter names this span contains".
Degree = position of the last name − position of the first + 1 E is the fifth letter, B is the seventh → 7 − 5 + 1 = 3, so E–B is a third.
Diagram: counting letter names, not keys
The last row is the point: E and F sit right next to each other, yet the interval is a second. So "close together" and "low degree number" are two different things.
Listen: two widths of the same degree
Every step in this figure is a second, yet they are not all the same width — same counting, different sound.
Common misconceptions
- "The degree is just a number of semitones." Semitone count belongs to interval size, a different ruler. A third can be four semitones or three.
- "A bigger degree always sounds farther." A high degree only means the letter names span more. The perfect octave spans the most and is one of the easiest intervals to identify.
- "There is one D between C and E, so it is a second." Both endpoints count. Three letter names means a third.
- "Diminished seconds and augmented unisons are impossible." They are legal intervals with extreme widths — see augmented and diminished intervals.
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Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Sources
- 音程度数按音级名（含首尾）计数的定义，属乐理通则，各版教科书表述一致
- 本文行文为原创，未采用参考源句式
Used for fact-checking only; all prose is original.