[frankmcr]

Originally Posted by DesertTwang

For the key of G, he says there are the following chords: G major, A minor, B minor, C major, D major, E minor and F major. I think I understand how these chords come to be -- we use only notes from the G scale to build them, and that's why some are major and some are minor -- but what I don't understand is why the seventh chord in the scale is flatted. There is no F in the G scale, so the resulting chord should be F# major, not F major. But the instructor makes it a point that it's flatted.

But why? Why does this one chord get an exemption from the rule of using only notes in the G scale?

It doesn't. The youtube guy is wrong. The "seventh chord" in this case is F# A C, which is called F# diminished (not F# major!).