Emacs has some key commands involving pressing multiple keys at once that are sometimes described as “chord commands”, which can be pretty inconvenient to type. I’m using C-M-v to scroll down the other window, for example, and M-{ and M-} to move by paragraphs, which require the shift key. I also use M-< and M-> to move to the beginning or end of file pretty often. M-^ (M-shift-6) joins lines together, which I do regularly. M-% (M-shift-5) is search and replace, which I use pretty often. M-| (M-shift-\) passes the region to a shell command. C-M-w does “append-next-kill”, which is occasionally useful. M-: (M-shift-;) is the eval-expression command, which I probably use as often as M-x. C-@ and C-_ are common commands that would be similarly inconvenient, but fortunately C-SPC and C-/ do the same thing. I occasionally use C-M-left and C-M-right to move over parenthesized expressions.
Key sequences like the infamous C-x 8 RET, C-x 8 _ a, C-x RET C-\, and so on, are also inconvenient; of course, like the chords, they’re hard to discover; but also you have to type them in the right order, which slows you down, it’s a real pain to do one of them repeatedly, and they amount to a short-lived modal interaction, which causes mode errors.
So in some ways the chords are preferable, but they cause repetitive stress injury. Also, in one way, even the chords are not real chords: on a piano it doesn’t matter if you hit the G key 4 milliseconds before the C key or 4 milliseconds after, but Emacs definitely cares a lot about whether you press A and then Ctrl, or Ctrl and then A. So even the chords are slower than they need to be.
But there are about 132 keybindings in global-map and another 32 in
esc-map, plus more commands provided by one mode or another (apropos
finds 3685 commands currently loaded), and only about 88 keys on this
keyboard, most of which normally have to be used for writing. Most of
the ones that aren’t for writing (Esc, F3, Insert, the arrow keys,
etc.) are in very inconvenient places. So it would seem that
inconvenient chords or key sequences are inevitable.
But can we do better?
The home row has 12 keys on it, if we omit the nonstandard position of \, and there are another 24 keys almost as easily reachable above and below, plus the space bar, the )} key, and on this keyboard the >< key, for a total of 39. In a spectacular feat of perversity, this doesn’t include the number keys, Esc, Enter, Backspace, Ctrl, Alt, or the left Shift key. But it does include Tab and the worthless Caps Lock. (I usually press Alt with my spacebar thumb, so maybe we have 40 convenient keys.)
It occurs to me that a much more manageable sort of chord would be one where you simultaneously press some magic “command key” and one or more keys for the command. So, for example, Alt-Q might be one command (and should act identical regardless of whether you press the Alt first or the Q first), and Alt-Q-O might be another command (the same command as Alt-O-Q). So any permanent effects of the command wouldn’t take effect until you started releasing keys. (They could totally change your view, though, since that’s reversible.)
Here are the keys conveniently reachable by each finger:
If the left pinky is tied up with capslock, then there are 3 × 3 × 6 × 2 × 6 × 3 × 3 × 6 = 34992 possible capslock-based chord commands, and there’s an even larger number of chords accessible with Alt as the command key, but we probably want to limit ourselves to chords that don’t involve too many fingers, both due to human limitations and due to key jamming and ghosting. Even chords that involve only two fingers can be awkward; try Alt-E-X, for example.
A very simple sort of first-level command set is the number of chords that involve Alt, one key from the left hand, and one key from the right hand, since those are all guaranteed to be easy to type. There are 17 left-hand non-thumb keys (15 if we remove capslock and the Spanish-keyboard-only <) and 18 right-hand non-thumb keys, giving 306 commands. This is a promising number of commands, and I think that key jamming and ghosting won’t be a problem at all on any reasonable computer keyboard with Alt plus two regular keys.
You’d think that in 02021 keyboards would handle at least three, but in fact even without Alt, this keyboard gets key jamming between Q and S when A is depressed, between A and W when S is depressed, between Z and S when X is depressed, and so on. Perhaps more alarmingly, FGH, HJK, CVB, and VNM also form such jamming triples, even though they’re physically all in separate columns of the keyboard. It may not be a coincidence that these all include pairs of keys that are supposed to be pressed with the same finger (FG, HJ, VB, and NM respectively); the keyboard may be designed (using the term generously) for correct touch-typing technique. Still, it makes me worry that some common keyboard out there will jam on easy-to-type combinations like FJK.
I think that generally the difficult-to-type chords are difficult to type because they have fingers of the same hand two rows apart: QV, ZT, WC, XR, Y., but not QF, AV, ZG, AT, WD, SC, SR, XF, YL, or J.. I think this gives a large number of four-key chords in consisting of Alt with the thumb, one key or two keys in adjacent rows or the same row on the fingers of one hand, and one key or two keys in adjacent rows or the same row on the fingers of the other hand. Crudely I guesstimate that this is about five thousand combinations.