The name I use to refer to Chord Functions is Chord Feels. I think it's a better word that gets straight into the essence of what the word refers to. If you get a feel for these Chord Feels, and 7 of them are basically all you need, and to be really honest, 4 of them are the main pillar ones that contitutes generally something like 80% of the Chord Functions used in popular music. They are: The 1, the 4, the 5 and the 6. If you just learn how to remember what they sound and feel like in your mind alone, just like you can probably right now recall the flavour of a strawberry, a lemon, some chocolate and a coconut. If you learn what these 4 main, pillar Chord Feels FEEL and SOUND like, then you have an edge in learning how to speak music as a languge instead of just being able to "parrot" what somebody has written on a paper for you to play - and to play it EXACTLY like it says on the paper... and so on. (That way of playing I have often likened to kissing somebody, and then you say STO