Is it that modes are altering comments?
Thus A,C, Eb is correct and A,C,D# would be not the best. But if you construct dim7 chords you can build an dim7 on each tone of the tetrad A,C,Eb,Gb and transform this chord to D#,F#,A,C and all other enharmonic exchanged chords. That's why the dim7-chords are useful for modulation. – Albrecht Hügli 19 mins ago
Tim commented 18 mins later @Albrecht Hügli: A,C,E is no diminished chord ... (but this comment has been deleted, could be that Tim missred something)
@Tim: did I say something different? – Albrecht Hügli 5 mins ago Edit
@AlbrechtHügli - yes, before you altered the comment! – Tim 3 mins ago
I can't alter a comment of 14 min ago ... But something irritates me: I don't remember that I had written would be not the best. Is there a ghostwriter in here? – Albrecht Hügli 1 min ago
It might be that I had a typo and wrote A,C,E (what I don't believe)
But I trust Tim and I also can't remember that I wrote A,C,D# would be not the best