F# on the C major Scale, explained

[mdecks]

C major is the key with no sharps or flats.
So why is there an f# on almost every piece in C major?

Well, the answer is in the piece's harmonic progression.

For a piece to be in C major, we need the C major chord to be the I. The I only feel as a I if there's a V7 before it (G7) and if we have the 7th degree moving to that 1st degree (B -->C). That G7 makes the C major stronger when it resolves to it.

But how do you make the V7 (G7) stronger? You use the V7 of that V7 (V7/V). In this case you use the V7 of G, and that's D7.

D7 has an F# in the triad (the 3rd of D) (F#--> G works as the 7th degree going to 1st)

And there's your F# on C. Every time (almost every time, we should say) you see an F# on a C major piece, the harmonic progression is going through the V7/V (that's D7). So look for the D, the A and the C in the rest of the harmony and you'll probably find them (D7 = D F# A C).

Ok... Why is there also a C# on C major then???

mDecks

[thirdcreed]

V7/V7/V! OR V7/ii OR if its part of F#7 V7/vii OR V7/V7/iii Or many many other options.

A V7 will in most cases tend to lead to the chord 5 notes below it in the scale. I.E. G goes to C (G-5,F-4,E-3,D-2,C-1). V7's can be used in this capacity on any part of the scale not just dominant. So E7 with a g# in it can lead to A minor. and then on to the rest of the progression, it really throws people when you include V7's of some of the harmonies already found in the piece.

V7's are also identical to another kind of chord called an German Augmented 6th chord. This chord will always lead to a half step below the root of the chord. So a G7 would lead to F#. The chord must resolve with the seventh and the root resolving up and down respectively to the F#. This is much more visually obvious on a piano. If anyone has any questions about incorporating German augmented 6th chords (Gr+6) into their songs let me know.

Great post mdecks. I'm kind of a theory nerd, and I enjoy talking theory with people, its definitely a worth while study.

BTW, another possible reason for the appearances of a chord in a song that is obviously rooted in c is that you are playing a c lydian scale.