It's just about harmony. ignore all the yammering about 16th century counterpoint, it's dead simple, although it takes a bit to explain.briefcasemanx wrote: Wed Aug 18, 2021 5:45 am I've watched a ton of YouTube videos explaining modes and I still don't get how to tell what mode a song is in.
The notes are the same between the modes of the same key, are the chords different? If the chords are the same I have no idea how anyone would say a song was played in certain mode.
when we chuck a bunch of chords together, a few things can happen, but one of the big ones is we get what sounds like a tonic chord (i.e. home), usually major or minor. other chord qualities (diminished, augmented) are just bad at being home chords, they want to move, so that's what we're stuck with most of the time: a major or minor tonic chord.
now we could go ahead and make up some scales that fit a major or minor chord, and write some music and say our song is in such and such a 'mode', but the thing is something is only the tonic when it sounds like the tonic. chords derived from the rest of the scale have a lot to do with making that happen. to put it bluntly, major scale harmony turns out to be really good at saying "this here is definitively the tonic", while the modes are slightly flakey - they need either a little finesse (i.e. avoiding stuff that points to the relative major, like its V7 chord) or they need chromatic raising/lowering of notes, which just so happens to make things sound a lot like they might sound if they were in a major/minor key... thus our major/minor key system becomes Kind Of A Big Deal in the evolution of western music.
left over we have a few modes derived from the major scale, two with a major tonic (mixolydian, lydian) and two with a minor tonic (dorian, phrygian). these have characteristic notes that distinguish them from good old major and minor. lydian it's the #4, mixolydian the b7, dorian the 6, phrygian the b2. now, finally, here's your answer: if those notes feature prominently melodically/harmonically AND the tonic actually sounds like a tonic, you might be justified in saying a tune or a part of a tune is in one of those modes. if those notes appear briefly, it's more likely there's just some borrowed chord stuff happening. if the tonic doesn't sound like the tonic, you're just in a misspelled major key. but wait, when is something in aeolian? same problem - you're probably actually in the relative major. if it sounds like a minor tonic and nobody ever plays a raised seventh, more power to them.
but that brings us to another big thing that can happen harmonically, especially in pop music and four chord loops, is the tonic is actually ambiguous sounding, or there are multiple possible tonics competing for attention. i.e. there is no here-this-is-definitively-the-tonic thing happening, harmonically, but there's not necessarily anything wildly chromatic or 'out-of-key' sounding, either. with chord progressions like that it doesn't actually make sense to talk about them being in a major/minor key OR a mode, we just don't have much of a formal system for it yet, so we're left with square-peg-round-hole analysis.
And no one tried to teach him counterpoint, mate. He was long gone when that discussion took off. You are shouting in the woods.