I was taking a look at "How Deep Is Your Love" by Bee Gees, and had a question about the verse progression. Do these 7, 9 , and 11 chords have a practical purpose? Or are they just for some extra flavor? I'm wondering if I should consider these scale degrees in my progressions more often. Here's how it looks:
Functionally, the extensions aren't changing the chord itself. A dominant chord works the same way regardless of whether it's V or V13(♭9,♯11). That said, usually the chord F/G isn't analysed as V11. There's certaintly no harm in learning how to use extensions, however, as they do add a certain colour to progressions.
They don't change function, they change colour.
I'm going to use a simpler example than the Bee Gees, because this ought to be recognisable from just 2 chords, once we add the tension.
OK, yes, it's "just flavour" but... try playing [at perhaps 70-80bpm, quite slow, simple crotchets will do, pedal down is nice] one bar of the chord A Maj [no inversion, simple root triad] with a simple bass note one octave below, then one bar of B Maj, similar configuration, round & round, one bar of each.
OK, it's 'fine' but it could get dull quickly. It also somehow sounds like we're changing key every bar... so let's fix that...
Let's add some flavour - in this case not only flavour, but tension... see how this almost forces the next chord...
Same bar of A, bar of B... but this time, only play B in the bass, never the A.
The B in the bass against the A Maj in the right hand makes this a B Maj 11, or you might prefer to call it A Maj/B, but the result is the same.
Tell me you didn't recognise that famous intro in one bar.
Once you've recognised it, you can change the simple crotchets to the slightly more complex timing the record had, it's not much of a stretch.