Notes for simple progression

Question

I struggled a bit to find a good title for this question since I can only really describe it with an example.

I have been spending some time on chord progressions and improvising and would think that this is a simple melody in C major using a I IV I progression:

X:1
M:4/4
K:C
|"C"C2D2E2F2|G2A2B2c2
|"F"d2c2B2A2|G2F2E2D2|"C"C8|

The notes all belong to the key of C as I would expect.

Now consider this melody over the same chord progression:

X:1
M:4/4
K:C
|"C"C2D2E2F2|G2F2E2G2
|"F"F2G2A2_B2|c2_B2A2F2|"C"C8|

To my ears, the melody demands the flat b in measure 3 and 4 and doesn't sound right without it. Likewise in the example above, the b in measure 2 and 3 only sounds right to me when it is natural.

So my question is why does one of these two simple and fairly similar melodies seem to require an out of key note?

Does the second example actually change keys and is not the IV of C major but the I of F major? If so, is there a logic to what enables this (in terms of music theory)? It must lie somewhere in the way the melody moves I guess.

It seems like I am missing some fundamental piece of knowledge and would be happy if someone could direct me to where I can learn more about this (terminology, links).

Edit: I can't seem to get SE to print the melody along with the chords the way I want. Trying to fix this.

Answer 1

This is more an issue of aesthetics and "indoctrination" into the expectations of Tonality than a core music theory issue. I prefer B-natural to B-flat in the second melody, but I've also had a great deal of training to expect that sound over the Bb. But in either case, it's an aesthetic preference, and both notes can be justified.

That said, I'll attempt an interpretation of how you describe hearing the two melodies.

• Melody 1: This is unambiguously a C major scale up and down. Anyone familiar with a C major scale will understand how to hear it. The strong-beat notes (i.e., beat 1 and 3) over the F chord are dissonant with the chord, but this is mitigated by the familiarity of both the chord progression and the scalar melody. Also, each of those notes is followed by a chord tone, so functionally, they're just accented passing tones, which is a familiar sound in Tonality.

• Melody 2: In measure 2, rather than continuing down the scale, the melody moves back up to G. This makes for the C chord to be easily heard as the dominant chord of F. This is reinforced by the melody landing on F and then placing A on the next strong beat (beat 3). Beat one of the next measure completes the outline of the F major chord. All of this together draws the ear strongly toward hearing F major as the new key.