My short answer is: No, it's not necessary... (necessarily).
Music theory can give you an understanding of how music can work. Learning about music history can be pretty useful because simply knowing bits of trivia and exposing yourself to all kinds of different music is great for inspiration. However you don't need institutionalised education for either of those things.
Just keep writing, listen to lots of music, and get feedback on your stuff. Most of it is getting comfortable with the medium and finding your own "voice."
I have a BS in music and I tell everyone this. Learn everything up to secondary dominants, which in college curriculum is most likely just Music Theory 1, a single semester. After that it gets into the weird stuff that you'll never use as mentioned above.
Hmm, I don't completely agree. Augmented 6ths, jazz theory, alternative scales/modes, rhythmic tension/resolution - there's some pretty neat stuff to learn from those things, even if you don't end up using any of those techniques in your own compositions.
Anyone looking to start really exploring music theory beyond the basics (particularly harmony), I point them in one direction: J. S. Bach... and then work your way along from there.
EDIT: OH, the writing down thing... uhh, well if you don't know music notation, record yourself singing, jot down the idea some other way (using just the note names, or the shape). Have something readily on you at all times (yeah this sounds a bit obsessive, but ideas can come at you at any point). I used to always keep a notepad on me (tho nowadays I just use my phone and make notes).
Last edited by Fearofdark (Mar 13, 2015 11:03 pm)