My guitar teacher has given me the assignment to compose a song that uses Major 7th chords 'cause we discussed them the previous lesson. Since I am not used to using these I was wondering if anyone could give me some tips when to use 'em and why they sound good or bad at a certain place in a song. I'm rather new to writing my own songs, I know how major and minor scales are made and how to make chords using a certain scale and that certain progessions sound good (I-VI-IV-V and stuff like that) and I can sometimes add a 7th but other then that I don't know all that much about music theory yet. Thanks in advance!
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In major keys, you can use the maj7 at the I and IV chord.

Also, V7 leads great to Imaj7. In case of G7 -> Cmaj7: GBDF -> CEGB. That's just one whole step movement and a half step movement, with two voices staying at the same place.

Other than that, just use your ear! I can't be any specific here.
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I would basically use a Major7 chord wherever you would use a major chord but would like a minor sound to the song.

I'm sure someone will come along and say "NO, FOOL!" but that's how I would do it.

EDIT: Except for the V chord, because that should be a dominant 7th.
A major 7th doesn't really give a minor sound, it just gives a different more flavourful and interesting sound. Although, I do see what you are saying since if you voiced it with the 3rd in the bass, you would have a Xm6 chord.
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