This sort of thing drives me up the wall.
“Leaps of a seventh are NOT allowed.” Why not?
“Are compound 5ths (i.e. an octave and a 5th) wrong ? YES, they are also illegal.” Why?
“You must NEVER write consecutives.” Why not?
This is useless information, and the way it’s presented is why newbie kids come up thinking that music theory is a bunch of worthless proscriptions that came out of nowhere, and that can therefore be broken willy-nilly to the effect of writing some seriously lousy “modern” music. The problem isn’t that the rules of harmony are arbitrary proscriptions; it’s that the teachers are inarticulate when it comes to explaining why they came about.
There are reasons for these rules — and no, it’s not illegal. It’s just that, if you do write compound 5ths, you will end up writing stinky sounding music.
But why? What is bad about music with these tendencies? Does it sound thin? Does it sound off-key? Does it not give the ear enough information to hold onto the melody? What is bad about it?
I’ve absorbed a ton and a half of music theory just from studying piano for so long. You can’t avoid it when you have the whole keyboard in front of you. Arp G-B-F with your left hand when you are playing something in C Major, and after a while you will start to notice when you arp D-F#-C while in G Major.
But even to me, these lists of Thou Shalt Nots are worthless. They don’t impart any information — why are consecutive 5ths a bad idea? What goes wrong with the music when one writes them?
(And we’ll conveniently sidestep the fact that there is indeed some gorgeous music that does use consecutive fifths, such as my beloved Ginastera’s second Argentine dance. The universe is a complex place.)
Ultimately, it becomes much easier to simply noodle around at the keyboard and use your ear to detect when something “sounds bad.” Chances are, it will sound bad because it has unwittingly broken one of the rules of harmony. However, what takes less time? Noodling and poking around for oneself, or reading a list of Thou Shalt Nots that doesn’t actually explain anything?
No wonder young kids in college think that music theory is useless and that they can write equally good music without the rules of harmony (BTW, they can’t). It’s presented to them as nothing but a bunch of things that are illegal for no reason whatsoever … even though there are good reasons why these rules are best adhered to. (Well, what the hell are they?)
Music teachers are worse than scientists when it comes to utterly lacking the ability to actually tell anyone what they’re doing. Geeks are geeks are geeks, no matter the discipline.