The principles/guidlines of classical, real music. Modern musicians tend to neglect music theory or have little knowledge of it. However, most knowledgeable musicians have a basic idea of theory. (Steve Vai and Yngwie Malmsteen to cite two)
Person 1: "Hey, play me a Em, FM, and GM in common time so I can put together a solo using the Em scale."
Person 2: "Whats common time?"
Person 1: "Oh great, I'm jamming with a moron."

You look like an asshole when you don't know music theory.
by Markus5273 October 4, 2005
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A class that explains the structure of music. You'll learn the difference between an A-sharp and a B-flat. Later you get into the rules of writing counterpoints and four-part harmonies, which are useless unless you write classical music, but are still good to know.
Music theory is the first music class I had to take in which I actually had to THINK.
by Mike the Ekim March 25, 2006
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A set of rules, guidelines, and terminology that musicians have come to agree upon over time.

Music theory mostly deals with the earliest music ever written on paper to music written in the late 1800's.
by The Drafted's guitar player April 29, 2005
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A great class and idea that helps people learn the rules of music, and other, greater ways to create a piece rather than just powerchords.

Also, something barely any musician has nowadays, and those who have none say that you "don't play from your soul" if you have knowledge of music.

These people are dumbasses.
Music theory taught me to create music in keys and gave me appreciation for all the epic classical symphonies everyone takes for granted now.
by motionless92 May 27, 2010
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A cancerous class at some schools where you learn useless shit.
-Hey dude why you looking so sad?
-Didn't you forget we have music theory today.
by Shrek_Our_Lord February 4, 2018
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Something that music snobs put a lot of attention into. In reality, unless you want to learn how to play like someone else instead of having your own style, music theory is useless. I mean, did the Blues guitarists who lived in the Mississippi Delta have access to music theory? No! And they laid down the innovations that modern musicians still use today! Kurt Cobain even said that music theory is useless unless you want to be coffee shop singer and is a distraction to making music your own thing. And he changed rock music for an entire generation!
Music student from Berklee (MSB): "What'cha doing?"
Me: "Playing the guitar. I just love this instrument so much. It's simplicity brings music to the masses. Every note rings 'Hey! You do not need expensive classes or fancy instruments to enjoy music!'"
MSB: "Well anyone will suck as a musician without proper music theory training."
Me: "So Jimi Hendrix, the Beatles, the Clash, Nirvana, and nearly every multi-platinum selling artists failed as musicians because they did not have any music training?"
MSB: "Well..."
Me: "And these chords that I am playing with the basic knowledge, regardless of the complexity of the composition, I have is shit because I do not have a musically trained background?"
MSB: "I guess so..."
Me: "Well I am not in debt to a fancy music school and I still know how to play music so you're the idiot. I win!"
by ThatOneGuyYouGrewToHate July 23, 2012
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Knowledge of chords, rythms, etc in the development of music, can make you a better musician but is not necessary
jimi hendrix, the greatest guitar player ever did not know shit about reading music. he played from the heart and soul, and thats what music is really all about. there are no "rules" you are supposed to follow to be a good musician
by . . . . May 23, 2005
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