I"m learning diatonics on guitar finally, and there are just some theory based confusions I'm having with these things:
Why are there only five diatonic scale forms if there are 7 modes not including hypo-modes?
The reason is because the major scale consists of seven notes. If you think about the jumps between notes, there is only a half step between the 3rd and 4th notes, and 7th and 1st notes. So the third scale form covers both Phrygian and Lydian, and the 1st scale form covers the Locrian and Ionian modes (Assuming of course that you're playing them over chords that resolve to their respective tonal centers, but then any scale form would technically be in the mode of the home chord, but that's another discussion 😉).
In western scales, there are a total of 7 notes. They repeat infinitely ascending, and descending.
You can break them up on the guitar into 7 convenient "sets" for easier memorization, but even each set can be made in multiple ways. For example you can have a scale set of 2 notes per string, 2's and 3's, all 3's, all 4's ect, and still play the same notes.
The hypo modes are something different, this is earlier than the modern 7 scales. These were more of a melody outline. The hypo versions had to do with the pitch that the melody ends on.