An interval is nothing more than the distance between two tones. It is often convenient to speak about music in terms of intervals, so it’s important that you know the terminology.
We distinguish between two kinds of intervals:
A melodic interval is the distance between two tones played after each other:

A harmonic interval is the distance between two tones played at the same time:

The rules for both types of intervals are the same.
The problem we are trying to solve is: If you have two tones, then what is the interval between them called?
There are several ways to approach this:
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