Why was the Ctrl + C key sequence selected for copying text, however Ctrl + P was not selected for paste in Windows?
Notice that C-copy, X-cut and V-paste are next to each other on the keyboard. Also they are very close to the ctrl key. if a user copied something to the clipboard, the next most probable action would be pasting what was copied. So compared to P, while it makes sense as a language, but from a HCI perspective. it'll be easier on the hand and fingers to go for ctrl+V
The whole hotkeys issue is a good example of the "intuitiveness vs efficiency/ease of use" trade-off. Yes, it would be very nice to have all our actions mapped to a key that begins with the first letter of the actions. It would be intuitive and easy to remember.
- Many actions have the same first letter. Of course you can then switch to the second, or another "representative" letter, but the deeper you get, the less intuitive and memorable it becomes.
- While it's possible that the above can be managed within a specific app (if it's small enough), it becomes impossible once you take into account that you're often using a number of apps at the same time. For instance, you're in Gmail which has some hotkeys, but it's running in a browser, which has its own hotkeys, and the browser is running on an OS with a different set of hotkeys. And you might have something else actively running, like a music player.
- Users speak different languages. Some languages don't use the Latin alphabet, in which case the mapping is useless. What's worse is that the languages that do use the Latin alphabet might have a different action "intuitively mapped" to the same letter, in which case the mapping is worse than useless - it's actively confusing. For instance, the Dutch word for "print" is "afdruk", so they'd map it to "Ctrl+A", which already has the standard meaning of "select all".
- Many actions don't have a very clear name as such. Using "ctrl+[" and "ctrl-]" increases or decreases the font size in a number of apps. Some people would say "increase/decrease", others would think it's "smaller/bigger" font, maybe others would use something else. There's the language problem again.
- As Ameen mentioned, many actions are logically paired, and since hotkeys are usually used by power users, we can assume that placing them together would be more important than making them easy to remember. Ctrl C/X/V are located together. The +/- and ]/[ example is another common one. A classic one is using WASD instead of the arrow keys for navigation in computer games.
- Once you begin using modifier keys (ctrl/alt/shift) you get to a situation where some combinations are impossible to press unless you're a career pianist, especially if you don't want to drop the mouse in order to do so. So you'll go by location again.
There's probably a bunch of other reasons too.
According to this Wikipedia article, the Apple Lisa and Macintosh were the first computers to map those functions to key combinations, along with Undo. They basically used the keys closest to the 'command' key. I'm not sure there was any other logical reason other than proximity on a standard QWERTY keyboard.
According to this article, the original cut/copy/paste paradigm was originated by program designers at Xerox Parc.
Some imaginative answers here - and the real solution is Wordstar, which was published in 1978.
In those days of CP/M, there were no cursor keys, so control-S was used by Wordstar for cursor-left, control-D for cursor-right, control-E for up and control-X for down by one position/line. CP/M had allotted control-P to "print the text being returned on/off" so you could get a copy of a report-to-screen by pressing ^P and then trigger the process by pressing "return" (got renamed "enter" later) - no graphics in those days - all character!
You'd notice that these keys form a convenient "diamond" on a keyboard. When special cursor keys were introduced, some keyboards had them laid out as a diamond rather than the current one-over-3 layout (and that seemed really odd when it first appeared.). As well, the control key was just to the left of the A key on many keyboards, which made using that diamond easy to type while leaving your hand on the "home row".
Control-A was back-one-word, control-F forward-one-word; control-R and Control-C moved by "one screen" (usually about 11 lines) up or down.
So, the next outer ring of characters is simply the original "diamond" on steroids.
Precede each of these with control-Q and you got to move to beginning/end of line, top-of-screen or return-to-where-you-came-from (^Q^X)
Copying and pasting involved a sequence of keys - ^K^B...^K^K...^K^C. These were ^K^B - mark start of block, ^K^K - mark end-of-block and ^K^C - copy-here (you would be moving the cursor between these sequence, obviously.)
This was cumbersome- but a whole lot easier than handwriting or retyping (although as late as 1986, we still had a "word-processor operator" who would retype documents because she simply refused to listen for long enough to be taught how to edit stored documents.(Joy, her name was - and a right misery, too))
As cursor and paging keys became more common, the requirement for ^S and its friends faded, and the keys were allocated other tasks by the manufacturers of newer WP programs. The "diamond" idea was hard to shift - well, no-one really tried AFAICS, so ^C became copy, and the next obvious letter for reverse-of-that was ^V, since ^P was allotted by CP/M. Sure, we were no longer using CP/M but it's difficult enough to get people to learn keystroke-sequences - don't ever try to get them to unlearn them once they've taken root...
Hence, ^C - ^V. Diamonds.
The C key is comfortably positioned relative to the Ctrl key; that's [likely] why it's been chosen for the Copy shortcut. The P key, on the other hand, is too far away from the Ctrl key.
On a QWERTY keyboard, the C key is on the row above the Ctrl key. You can press both with your left hand while it remains in a natural and rested position, even if you have small hands. That is, your left small- or ring-finger (depending on the keyboard) can press Ctrl / Cmd and your left middle- or index-finger presses C without having to reach.
The Z, X, and V keys are immediate neighbors to C and are used with other keyboard shortcuts for the same reason.
You can, in theory, press the Ctrl / Cmd key and the P key with your left hand, but you have to flex your hand. You could also use your left hand to press Ctrl and your right hand to press P but removing and then returning your mouse/track hand is inconvenient.
Originally there were two standards:
The Apple Standard: "zxcv" + Command (although i didn't find a good reference for when the "zxcv" started, it seems that the P as print for Macs started around 1989 http://www.asktog.com/TOI/toi06KeyboardVMouse1.html before it's P for Plain)
The IBM Standard: Insert, Delete + Control Keys (Control, Alt, Shift) http://publib.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/F29AL000/2.2.106?SHELF=ceesl002&DT=19921204095534 or wikipedia: https://en.wikipedia.org/wiki/IBM_Common_User_Access)
Microsoft products started with the IBM Standard as they "developed" their OS to run on IBM computers. With time they choose to adopt the Apple Standard as it's popular and easier to use. The true origins of the 'V' as paste are almost impossible to recover, but it may be argued that it was both a usability problem (get it close to the other common text shortcuts) and a many functions for one key problem (P for Print or P for Paste  also P for Plain (remove bold/italics/underlines) [/edit]).
Moreover an Apple Computer had the command key close to the Alt, Control and Shift Key (https://en.wikipedia.org/wiki/Apple_Keyboard#/media/File:Apple_Macintosh_Plus_Extended_Keyboard.jpg), so it may be argued also that while any four close by keys could be used for the given functions, these keys would give better usability if closer to the command key. Of course one could argue that both C and X are very similar to their actions, making that position the best suited for the action set.
In the end it's major conjectures(theories) as of why the first Apple OS Computers of the nineties used these shortcuts, but probably it's simply because someone thought that would be a very useful set to have and would be used so much that they must be close to the Command (Control in windows came much after).
PS: If someone can find the Apple Interaction Guidelines of 1984 to 1990 it might be solved.
One thing that no one has mentioned so far: none of these other basic text editing shortcuts match the first letter of their actions. They are:
- CTRL + Z for "undo"
- CTRL + X for "cut"
- CTRL + C for "copy"
- CTRL + V for "paste"
Maybe you could stretch that and say "eXtract" instead of "cut", but that word is not really used anywhere for that shortcut. On the other hand, all four of these shortcuts are positioned right next to each other in the bottom left corner of the keyboard. So CTRL + C is rather the odd one out.
Also, you are only looking at this from an english/american viewpoint (as a lot of user interface designers sadly do) and forget about all the other languages. In most of the other languages the names for these commands start with other names and would thus not match either. Considering that there are more computer users worldwide who are not English native speakers, focussing too much on an english/american view can alienate your other users. This is actually a very common mistake, so there are e.g. some games or other software (e.g. the Atom editor) that don't work properly with other keyboard layouts than the English one.