I watched a lesson where the teacher said that if we want to harmonize the fourth grade of C Major with 7/11 chord, we should use #11 (i.e. F maj 7 #11). I could not understand the reasons well. Is it because of that flat in F? If so, is this an exception?

Regards, Kiko

• .. the fourth grade of C? Explain this, terminology, please. Dec 8, 2016 at 12:55
• @NeilMeyer I assume the OP means "(scale) degree". Dec 8, 2016 at 22:50

I've never heard that particular terminology ("fourth grade of C") either, but I'm guessing the rationale is this:

If you're harmonizing an F chord, normally the key of F major has a B-flat. However, since you're harmonizing an F chord in the key of C major, you will not use a B-flat, since B-flat is not in the key of C.

As such, this F major chord will not have a B-flat, but rather a B-natural, which is the #11. (Similarly, the maj7, E-natural, is in the key of C as well.)

It may be helpful here to note "the rule of seven": if a chord extension is higher than 7, just subtract 7 to get a quicker idea of what interval that extension is. For instance, if you have trouble remembering what an 11th above a pitch is, just think 11-7=4 to realize that an 11th is really just a 4th above. (Obviously there are some concerns here with octave displacement, but this is just a fast way to determine the pitch name [or pitch class, if you've heard that term].) Similarly, a 13th is just (13-7=6) a sixth above.

• Sorry, not a native speaker, and I wrote it quickly. By fourth grade of C major, i meant F lydian ( : Richard, thank you for the explanation! ( : Dec 8, 2016 at 13:03
• No worries, your English is terrific! Dec 8, 2016 at 13:19
• I reckon the chord is called 7/#11 rather than 7/11, for the reason you state. It works for all keys, just that with root F in a chord, the Bb gets cancelled by the # to be just plain old B, which possibly caused confusion. '4th grade of C' must be IV, but a strange nomenclature indeed. Not sure if Lydian is relevant? +1.
– Tim
Dec 8, 2016 at 16:57

I think the teacher is just alerting you to the fact that when a 4th (11th) is ADDED to a chord (as distinct to being used as a suspension) it's a lot less painful when sharpened. And that this, a IV7(#11), is a particularly nice sound! Note it, and add it to your box of tricks.

• (Note that OP mentioned Fmaj7, so if we follow that it would be E-natural instead of E-flat.) Dec 8, 2016 at 19:01
• Perhaps. He mentioned 7/11, and '7' in a chord name is minor unless stated otherwise. But there are so many systems of chord description... Dec 8, 2016 at 19:12