No problem with that. That's the issue. Can a "tonic" be dissonant and still have a tonic function? Certainly we've learned to accept maj7 chords (classical dissonances) as tonics. I think that's a good argument. I wouldn't argue with that. It's only the use of the word "tonic" I have a problem with. Yes. No disagreement there. I know I'm being a pain here, but I'm trying to preserve some consistency in the definition of terms so we can all know what we're talking about. The word "tonic" has a narrower meaning than just a "nice chord to end a song on". "Tonic" means "I" or "i". We can end a song on a IV or V, if we want, anything but I - it can definitely sound as cool as ending on a m7b5. Ending on IV doesn't mean it thereby becomes I. Subdominant and tonic mean different things. Absolutely not. The "rules" are not about what you can and can't do. I've never suggested any such thing. I said "common practice, not laws." The rules are just what you call whatever you do, so we all know what we're talking about. Terminology has to be consistent, or there's no point in using it. The more a word can be used to describe different things, the less use that word is. That's great. That's what we all do with music - as much or as little as we want. But don't treat terminology the same way. Do whatever you like, Just call it by the right name when you do. Or - if music theory doesn't yet have a name for it, invent one. In this case, there is no need for a new term, and no need to misuse an existing term. A m7b5 chord is a minor key supertonic, or possibly a major key vii (leading tone chord). It's not a "tonic", even if you end on it and hear it as stable. If, OTOH, as I think we were talking about here, you use certain extensions on a major tonic so that it resembles an inverted m7b5 (Bm7b5/F in key of F major), then it's a type of lydian chord. F6#11, if you like.