Don't take my word for it, but I think you looks at the chords or notes used, lets say a riff using notes a, d, e and f in it, you'd find a scale containing these notes in it, e.g c major or d minor. I'm possibly wrong though, check to see if theres a lesson on it or another thread, I'm pretty sure this questions been asked before.
Ive always thought of it as the base note or chord of the song. In most of the music I listen to (metal/hardcore) the key is the open E (or whichever tuning the guitar is in, usually D or C).

For example, in standard tuning (EADGBE) a song that started with a the below power chord and riff would be in the Key of E minor. The scale is minor and the key is E.

. .

The key is always where the music returns to when a section or riff repeats. Some bands change keys within the song, so technically in those songs there are more than one key, unless the change is only temporary and the original key is returned and repeated again. It sounds complex but it makes sense in my head
Last edited by ballsout at Mar 11, 2008,
Shouldn't a Key of the song pretty much be the root not you play?

For instance in AC/DC High way to hell it would be a A then wouldn't that be the key of A?
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ballsout was on the right tracks i think. It is basically where the song resolves.

you can figure the key out by spotting chord patterns. In C major, the chords are-


if you spot those chords in a song, it will usually be in C or Am.

the common things to spot are -

2 major chords a whole step apart - these will always be the 4th and 5th of a key
dominant 7 chord - this is the 5th of the key
2 min chords a whole step apart - these are the 2nd and 3rd of a key.

unfortunately it is not usually this straight cut, but that is diatonically correct.
Actually, the root note is not always the key of the song.
Roots and keys can be very different.

Branny posted a lot of ways to help determine the key your in, but it all goes down to music theory.

Keys are ultimately derived from the use of the major scale.

For example:

If I apply the major scale to this progression, the only key it could naturally be is D major (that means the common notes are in this key, not this root". So if you jammed along playing notes in the D major scale, you wouldn't be out of key.

Even though I know what ballsout meant when he showed this diagram, this is not E natural Minor, the 4th fret on the A string is a C#. Because the bass note is E, we can think of it as Em with a raised 6th note, C#. The melodic minor scale uses a raised 6th and 7th note in the minor scale, so if you knew that, than you can justify playing in the key of E minor, but it would be a good idea to use the raised 6th note (and raised 7th for that matter).

If your still confused, say so.
What branny posted earlier was actually a helpful peace of information.

This is the major scale, in chords:


you should master playing them ascending and descending. When you play with this chord formula, you are playing correct chords for every possible note in the scale, and staying in key.

Note that this is set up for C major

A universal way to think of it is:

There are seven notes in the Major scale...
And each one of those notes are assigned a chord type

1 - Major Seven maj7
2 - Minor Seven m7
3 - Minor Seven m7
4 - Major Seven maj7
5 - Dominant Seven 7
6 - Minor Seven m7
7 - Half Diminished m7b5
Learn your scales. I don't mean to be a dick, but that's the surest way to determine keys or tonal centers because a lot of modern music does not follow standard progressions.

But learning the major progression like everyone has listed, is also good........for now.
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