flatted fifth vs sharpened fourth

[synaesthesia]

Pocket changes. My pianist turned me on to these. Great little folios. The first I have seen where all the b5s I used to know in tunes are notated as +4s.

[Stumpy]

I should think that it is not in place of the b5 but rather in place of the #11. Since the 11 is not used in a major chord - ever (as it is horrible sounding) - without an alteration (usually the #11) and the 4 is the 11 just as the 2 is the 9.

Some chords for you to look at ...

Cmin7 add2

Amin7 add4

those sound great, but if they were major chords...try that for a second.