I need this clarified in my head because it keeps confusing me..

a perfect fourth is E to A, or a perfect fourth could be F sharp to B. I keep getting confused if this changes depending on the key of the song and also i get confused about it in chords...i understand majors have a major 3rd and minor chords contain a flattened third, but how does this relate to what key you are in.
I am just starting to learn mudic theory but i dont think f sharp to b is an interval becasuse there is a whole step every other not but on f there is a half does that make sense if not forgive me im just starting to lean music thoey after 10 years of playing
F# to B is 2 1/2 steps which is 5 semitones, so yes it is a perfect fourth...I think, I'm a noob player but I know a good bit of theory
Last edited by hendrixism at Feb 19, 2009,
a perfect fourth is always 5 semitones away, don't listen to youngncy at all.
yes e to a, and f# to b are perfect fourths. and a perfect fourth doesn.t change from key signatures
E to A will always be a perfect fourth, doesn't matter what key. and yes, F# to B is a perfect fourth, I do believe. intervals between two specific notes are what they are, and they don't change with different keys.
yup, you're right about the perfect fourths. every key works the same way. they just contain different intervals depending on if they are major or minor. so the interval pattern for A minor is the same as for B minor, C minor, D minor, etc... you just start on a different root note.

as for your question about thirds and chords work... if you are in a major key, it means that all your chords are derived from the notes of your major scale. let's use C major and C minor as an easy example.

for C major, you interval pattern is: 1 - 2 - 3 - 4 - 5 - 6 - 7. nice and simple, no sharps or flats.

C D E F G A B C

to get your chords, you just take each degree of the scale and add thirds to it, using only notes from the scale. so to make the first chord, you'd use C, then go to the next third. a minor third is three semitones, and would be an Eb. since Eb is not in this scale, you would have to use E, which is four semitones away, or a major third.

to complete the chord, you need to add another note, a third away from your third, if that makes sense. three semitones from E takes us to G, which IS in the scale, and happens to be our perfect fifth. so you've got a root, a major third, and a perfect fifth, which we derived by stacking thirds.

if you start on the next note of the scale, D, you get a minor third and THEN a major third. D, F and A. If D is the root of your chord, F is the minor third, and A is the fifth, which of course is the formula for a minor chord.

applying this to the rest of the scale, we get:

C major (major third, minor third)
D minor (minor third, major third)
E minor
F major
G major
A minor
B diminished (two minor thirds, giving the chord a flat fifth)

but it's not as hard as all that. we're in a major key, and you'll notice that (with the exception of that last chord), all your perfect intervals are used as the roots of the major chords, and your imperfect intervals are the roots of minor chords.

in short: a major key has major chords on the I, IV and V, and minor chords for the ii, iii and vi.

for a minor key, things are basically reversed.

your interval pattern for C minor would be: 1 - 2 - b3 - 4 - 5 - b6 - b7, giving you the notes:

C D Eb F G Ab Bb

if you make your chords from stacking your thirds, you end up with:

C minor
D diminished
Eb major
F minor
G minor
Ab major
Bb major

as you can probably see, in a minor key, your perfect intervals are the roots for MINOR chords, and most of your imperfect intervals are the roots for MAJOR chords. the position of the diminished chord has changed, but that's a few more paragraphs. i'll post it if you're still curious.
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