Originally Posted by: Jolly McJollysonWell, I hate to be a burden, because I know you're right and Joe Novice is wrong, but A-C isn't an augmented second. A to B# is an augmented second, and don't go all "but those are the same pitch value" on me. I know, I know, and I hate to be anal retentive, but A to C can't be a second, only A to some form of B can be an ascension of some kind of second. A to some form of G would be a descension of some form of second, and A to C would be an ascension of some form of third, etc. I see the point you're trying to illustrate, but could you try to illustrate it in a way that doesn't involve calling A to C a second of some form? Maybe replace the C with a B#?

Hey Jolly, I think you missed the part when I said...

Here is an example of this in the key of A.

So here is the A major Scale:
[A-B-C#-D-E-F#-G#]
In relation to the root, "C#" is a Major 3rd, and what happens when you flat a major interval?...you get a minor interval. So if you flat the "C#" you get a C natural, which now is minor 3rd.
Now "B" is the major 2nd, right? and what happens when you sharp a major interval?...you get an augmented, so raise the "B" half step, and you have a "C". Thus, A-C is an augmented 2nd.
That is why I stated:
*[1-b3]=A-C
*[1-#2]=A-C
Both result in the same notes(A & C).
But the first is a Minor 3rd interval.
The second is an Augmented 2nd.

I see where you got confused. That example is not in the key of C.
It is in the key of A major.