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I am learning a song that has a V sus 4 chord and then in the guitar version of the same song the person who notated it used a Isus2 chord instead... I realize they sound very similar. Are they the same chord? Are there any other doubles of this nature in normal diatonic chords?

  • No, it's not the same, and strictly speaking IVsus4 isn't even completely diatonic, because the sus4 is a flat seventh of the scale. Are you sure you don't mean V sus4? – piiperi 2 days ago
  • yes sorry, I changed it... of course how silly of me, the 4th is lydian mode which has an augmented 4th :) thank you for your intuition – armani 2 days ago
  • The title is still wrong. :) – piiperi 2 days ago
  • that edit button is a godsend – armani 2 days ago
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V sus 4 is very similar to I sus 2, just the bass note is different. You can think of Vsus4 and Isus2 as being inversions of each other.

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    …because using sus rather than add removes the third each time, which would otherwise make the distinction clearer. – Tetsujin 2 days ago
  • do I intreprete correctly: GCD compared with CDG? wouldn't Csus2 contain a 3rd? – Albrecht Hügli 2 days ago
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    @AlbrechtHügli - no sus chord contains the 3rd. That's the whole point - the 3rd is suspended. Add 2 or 4 is different. – Tim 2 days ago
  • @Tim: Ok. I thought it would resolve to the prime. Thanks! – Albrecht Hügli 2 days ago
  • Pretty sure I'd already said that :P – Tetsujin 2 days ago
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Here is a pedantic answer from a music theorist: They are both the same and different.

They are the same in terms of intervallic structure. They both contain a fourth, a fifth, and a second, which is a pitch class set referred to as [0,2,7] or Forte number 3-9. As such, they sound basically the same when heard in isolation; to me, they have a characteristic "open but pungent" quality. Another way to say this is that they are the same sonorism.

They are also the same in that they are both quartal chords (chords that can be formed by stacking fourths). This sort of harmony system was popular in the mid 20th century, the most famous example being the theme to Star Trek the Original Series.

That being said, they are also different in terms of functional harmony (a.k.a. Beethovian-tradition western tonalism, which is the basis of most popular music today). In the Vsus4 chord, the G and C form a dissonant fourth, while in the Isus2 chord, they are an inversion of a perfect fifth (see this link for the reason why). Therefore they have different tendencies and serve a different functional role in tonal music. The Vsus4 is a dominant chord, where the C will tend to want to resolve downward, while the Isus2 is a tonic chord that does not require resolution.

If you are analyzing music, you should consider the context when deciding whether a chord of this type is a Isus2 or a Vsus4. For most applications, these chords are considered functionally different.

  • I like the fact that you are actually addressing the functional differences rather than just saying they're the same. +1 – ggcg yesterday
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So I've learnt something again: The 3rd is missing in a sus2!

(like piperii says, the root will be defferent: I = tonic V = dominant)

Here are some good pictures explaining the situation:

enter image description here

enter image description here

https://www.piano-keyboard-guide.com/suspended-chords.html

  • Yes, with a 3rd it would be an add2. – ggcg yesterday
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Isus2 in key C consists of C D and G. The 3rd (E) is lost in favour of the 2nd (D).

Vsus4 in key C consists of G C and D. The 3rd (B) is lost in favour of the 4th (C).

Thus both have exactly the same notes. So it could be conceded that they are the same chord, albeit with different voicings. However, a I chord is root based, while a V chord is dominant. So they have different functions. Partially, it's up to the writer to decide which will be the 'correct' one in its position in a piece, so 'the writer' has the choice of name.

Usually, the root note will be the decider, so here, if C is better underneath, it'll be Csus2, otherwise vice versa.

  • Ok I understand but could we say they are harmonically interchangeable? So if I was composing on the guitar and the fingering might be easier for a Isus2 chord then I could just use that? I think this is why the sheet music notation changed the Vsus4 to a Isus2 in my sheet music. In the piano version it is always a Vsus4 chord but I think in that key it just was easier to play a Isus2 on the guitar – armani 2 days ago
  • Please don't assume that a writer of music must be male. – Greg Martin yesterday
  • @ armani: and mind that the e-bass will play the root note of the dominant chord ... when Vsus4 – Albrecht Hügli yesterday
  • @GregMartin - I'm not particularly assuming anything. And I certainly don't want a re-run of the debacle here over the last couple of months. I do try to be 'politically correct' but we must try to be grown up. I've edited for the sensitive amongst us. – Tim yesterday

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