When looking at the C7 chord, why are the E and b-Flat the guide tones. Typically the major guide tones are the 3rd and 7th of the chord. Maybe I'm goofy but thought the the 7 in a major chord would be B, not B flat! Can you or someone tell me what I'm missing here?
C7 means a C major triad plus the minor 7th. C, E, G, Bb. Cmaj7 has the major 7th. C, E, G, B.
Why does '7' mean 'b7' in our system of chord naming? Probably because the most common 7th chord in simple diatonic harmony is the one built on the dominant note. We take the shape of that chord as the default for 7th chords. Don't worry about it, just know that C7 (or anything7) means the minor 7th.
There are 4 oft used 7ths. Each has, unsurprisingly, a different name. Major 7 has the maj triad plus the maj7 note. CEGB. Minor 7 has minor triad plus min7 note. CEbGBb. Domninant 7 has major triad plus min7 (or b7) note. CEGBb. Minor major 7 has minor triad plus maj7 note. CEbGB.
The most used is dominant 7th, and can be explained due to the fact that the 7th part actually comes from the key in which it's dominant. In this case, F, not C That's where Bb lives). The fact that it features a lot means it has the simplest name. Why not?!
From a sound point of view, the E is the leading tone, pushing to F, and the Bb meanwhile pushes to A. Hence guide tones, Using the major 7 version of C doesn't have that decisive push at all.
I am not exactly sure what you mean by guide tone section but Here I go.
C7 is a dominant 7 chord not a major 7 chord. Dominant 7th chords have a strong tendency to resolve to the tonic.
C7 would be dominant in F major (F A C)
In F major B is flat.
So forming the dominant 7th on C will produce C E G Bb.
The E is the leading tone (7th note of the scale) in F major. E will strongly want to go to F.
Bb is the subdominant (4th scale degree) which tends to resolve to the third scale degree which is A.
I suspect that is what is meant by guide tones, since Bb and E are acting to harmonically pull the chord in a certain direction. The E wants to go up. The Bb wants to do down.