The (musical) key sequence is, as you already know, [2, 2, 1], 2, [2, 2, 1]. It is, therefore, very easy for you to work out the (physical) key sequence starting from any of the 12 (physical) keys of the keyboard.
Whichever (physical) key you start on, that becomes the name of the (musical) key.
We always start with the first (physical) key of the keyboard group, ie “C”.
We start each subsequent sequence from the 5th (physical) key of the previous sequence (hence the significance of the “Circle Of Fifths” that I touched on earlier). For example, the 5th (physical) key of the (musical) key of “C” is “G”. A neat way to remember them is C G D A E B or B E A D G C (depending on whether you go clockwise or anti-clockwise on the circle).
Wherever you start from you just repeat [2, 2, 1], 2, [2, 2, 1]. Simple.
You might (should?) have noticed that each sequence begins with the last 4 notes of the previous sequence. You might remember what I said earlier about “So, La, Te, Do” being just “Do, Re, Me, Fa” repeated. The second tetrachord (“So, La, Te, Do”) of one octave is the first tetrachord (“Do, Re, Me, Fa”) of the next octave.
So it all makes sense now, yes? The tetrachord is all you ever need.
I’ll also repeat here, though you already know it, that the 7th note is only a “half-step” short of the 8th note, and that the 8th note is actually the 1st note of the next octave. This is logical because it’s the last two notes of the tetrachord (the “Me – Fa”, duplicated as “Te – Do”).
This will be of MEGA significance later, when we come to “7ths”.
From this table you can easily identify your “1, 3, 5” chord pattern. In fact I’ve marked them for you. I’ve also marked the 7th, because we will be needing it soon.
Chord C: (physical) keys C E G
Chord F: (physical) keys F A C
Chord G: (physical) keys G B D
Do NOT try to memorise this table. That’s “school” style learning, and it’ll do your brain in. You already know how to create them (from 4 “half-steps” then 3 “half-steps”). So use the table only for a back check.
Meanwhile, you may (should?) have noticed that there is a steady increase in the number of sharps as you go down the list. C has 0, G has 1, D has 2, A has 3, E has 4, B has 5.
That will be of MEGA significance later (just tuck it in back of brain for now).
But … what happens after B? Things go a tad “squiffy” from there on because there are only 5 sharp/black keys. How is it possible for (musical) key F# to have 6 sharps? It’s not possible. Or is it?
Do you remember that a sequence cannot have a letter repeated? Well F# has an F already. That can’t happen. Luckily the black keys have dual nationality. So we rename F# as Gb. Oops! That means that the (musical) key of F# doesn’t exist. It becomes Gb. You may remember that I warned you that this would happen.
The same holds true of the next 4 (musical) keys: C# becomes Db, G# becomes Ab, D# becomes Eb, A# becomes Bb. All for the same reason. That deals with all 5, dual named, black keys.
By doing this we end up with keys that have a mix of sharps and flats. It’s much tidier if we change all their sharps for their flat alternatives. We conclude with all the (musical) keys between the “…” having “flats” instead of “sharps”.
Finally we have the (musical) key “F”. This contains 2 “A” references. Again, it’s not allowed, so A# becomes Bb. But the (musical) key “F” retains its name.
The new sequence is shown below. And if you read the list from the bottom up then you see an increasing number of flats as you go up the list.
This explanation is not at all clear when displayed in a vertical list like this. But when you see it in “The Circle Of Fifths” it will all fall into place.
Before we leave this page, let me resolve some of the contradictions I created.
There are only 7 chords:
ALL chords are named after the 7 white keys (C D E F G A B), thus only 7 names are possible.
There are only 12 chords:
the 7 above, plus the 5 black keys (which are also named after the 7 white keys)
(C#/Db D#/Eb F#/Gb G#/Ab A#/Bb)
There are dozens of chords:
Quite literally, because they come in 12’s. You know 2 dozen already: 12 Majors and 12 minors (and you know what a TINY difference there is between them).
Stand by for more, later.
All the keyboard blocks begin with “C”:
The exception is the “full size” keyboard. I told you it has 88 keys. The extra 3 on the left are A, A#/Bb, B. This is the one and only keyboard that actually begins on “A”.