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0 C7

C7 ( 1-3-5-flat7) is suppose to contain a G as its 5th right? So how does a guitar get away with this in open position?

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If the G string wasn't fretted, it wouldn't be a C7 chord, now, would it? (it'd just be a C chord) – Cole Johnson Apr 11 '15 at 5:48
up vote 27 down vote accepted

Two reasons.

  • You don't have enough fingers to play it.

  • The fifth is the most expendable note in a 7th chord (1-3-5-7).

Without the 7, it wouldn't be a 7th. Without the 3rd, it wouldn't be major or minor. Without the root, it wouldn't be the chord that it is. But the fifth doesn't contribute any vital property of the chord.

There is this other fretting option which gives you a G:

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great answer, thank you. Are there any other expendable intervals? Like, can you omit the 5th and 7th of a 11th chord? and it would be okay? – Vigrond Oct 9 '13 at 4:48
The fifth is usually the first to go, I think. But with an 11th chord, the 7 is still pretty vital, usually. YMMV. – luser droog Oct 9 '13 at 6:04
@Vigrond: If you have a bass playing the root you may omit that. – Ulf Åkerstedt Oct 9 '13 at 6:36
Once you get past 7th, theoretically, you need to keep that 7 in the chord. However, particularly on guitar, there are not enough fingers, or strings, or handy frets to play all of the 'required' notes.Often, you can put all of the notes in, but the voicing comes out sounding bad.So, put in what sounds good ! 9th needs 7 and 2, 11th needs 7 and 4, 13th needs 7 and 6, as a guide. – Tim Oct 9 '13 at 8:59
The natural 5th is the second most consonant sounding interval after the octave. Usually the next expendable interval is the natural 11th in case of a 13th chord (the 9th needs to be contained and so does the 7th). – András Hummer Oct 9 '13 at 11:18

One reason why the perfect fifth can be left out is that the note is sounded within the root. It's the second harmonic, so it's there anyway, albeit in a quiet way, although some instruments will let it sound better than others.

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thank you. I'm not sure if my basic understanding of music theory is enough to understand your answer. Are you saying the "C" note (root) has underlying "G" tones? – Vigrond Oct 9 '13 at 15:19
Yes, the fundamental note of C has - 1st harmonic C (octave higher), 2nd harm.G, 3rd harm.C (another oct.up), 4th harm. E, 5th harm. another G. Tends to be quite weak after that ! To find them on guitar, touch a string at 12th fret (1st h.) 7th fret (2nd h.) 5th fret (3rd h.) 4th fret, (4th h.) – Tim Oct 9 '13 at 15:44

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