When writing intervals on the staff, it is common to confuse intervals with the same number of half steps.
For example, one may accidentally write C to F# (an augmented fourth) instead of C to Gb (a diminished fifth).
Although both intervals sound the same and look identical on the keyboard, one is a fourth and the other is a fifth.
Fortunately, an easy three-step process exists to reduce the risk of this mistake.
Let's write a minor third from C.
First, write the generic interval on the staff. For this example, we will write a generic third.
Next, figure out the number of half steps on the keyboard. Since a major third is 4 half steps, our minor third will be 3 half steps.
Finally, compare the staff and keyboard results. Add any needed accidentals to the staff. C---Eb is a minor third.
For our next example, let's try a diminished seventh from F.
First, write the generic seventh on the staff.
Next, figure out the half steps on the keyboard. (Since a major seventh is 11 half steps and a minor seventh is 10,our diminished seveth will be 9).
Finally, add any needed accidentals. .
For our final example, we will write a diminished fifth from B.
First, write the generic fifth on the staff.
Next, figure out the half steps on the keyboard. Since a perfect fifth is 7 half steps, our diminished fifth has 6.
Finally, add any needed accidentals. In this example, no accidental is needed. B---F is a diminished fifth.