Intervals
Interval Quality
Yet, not all intervals of the same numerical classification are of the same size. That is why we need to specify the quality by finding the exact number of whole and half steps in the interval.
From any piano key to the next we have a half step:
Some seconds have 2 half steps or a whole step and some seconds have 1 half step. In the following example the second from C to D has a whole step while the one from B to C has only a half step:
The same thing happens with other intervals. That is why we need to specify the quality of the interval by finding the exact number of whole and half steps.