Why are the strings of a guitar EADGBE and the strings on a violon GDAE? That’s backwards. Why is this? Is there an instrument with the same setup as a guitar?
(No big words, No complicated music theory stuff, please, just a simple answer.)
The layout of fingers on a human hand can only be contorted into so many shapes, so I’m guessing it’s easier to make chords across four to six strings with this set up.
You could retune a guitar to CGDAEB and then try forming chord patterns.
I think that’s basically it, form follows function. Ergonomics. It’s not really backward, it’s just what it needs to be. From some meager research I gather it developed from lute tunings over a long period. And oddly enough, the open fifths tuning of the violin/mandolin family seems to be the minority. There are tons of instruments throughout the western world that use guitar-like tunings but not so many with violin tunings, and it dosn’t seem to show up very much at all in eastern music. You can, on the other hand, easily tune any of the larger mandolins and even the banjos in ‘Chicago tuning’ where you use the layout of the highest four strings of the guitar. This takes a bit away from the melody capability of the instrument, but it becomes a real chordal powerhouse. And of course, the ukuleles all use a variant of that, although the smaller ones have their bass string tuned up an octave higher so that the lowest string ends up in the middle, called re-entrant tuning. The electric bass, if I’m not mistaken, commonly uses the lowest four strings of the guitar tuned an octave lower. A great many Spanish instruments use variations of guitar tunings like the charrango, tipple, tres, quatro, banduria, bandolim, etc, etc. So guitar-like tunings show up all over the place. It’s handy, pardon the pun.
And building on Martin’s observation of a guitar tuned in fifths, not only would it be very difficult to play, but I imagine that would put disasterous tension on the intrument, so there’s probably a structural reason for guitar tunings as well. When all you have is wood and wire, I suppose you have to design around those limitations.
Oops, that’s way more than 100 words. Sorry. 
What he said. (Three words. I win.)
Robert Fripp’s “New Standard Tuning” is CGDAEG, basically an extended cello tuning. He’s been using it since 1984, and his Guitar Craft students were all trained in it, though i don’t know how many use it as their standard tuning.
He usually recommends Ovations, IIRC, which would be structurally more amenable to the tuning than most other guitars.
That’s very interesting. I suppose it would require a modern instrument design and materials. I was thinking more along the lines of how the instrument would have developed from original technology. I wonder if they could have done that 200 years ago?
Good point which I overlooked. Tuning up strings is only safe for about a tone, and tuning down more than a tone usually leaves the strings too slack. I wouldn’t want to do it for a long time, or to a good instrument, and beware snapping strings which can be dangerous.
However if it was playable with a human hand, I think guitar strings could be designed to any tuning - you just adjust thicknesses according to what you want.
It may be that as guitars, lutes etc evolved, the materials available reduced the tunings possible.
I think that’s probably the case. Instruments evolve around technology, and music evolves to exploit that. I saw an electric bass once with seven huge strings. It had lots of steel reinforcement and made use of advanced materials like carbon fiber. I got the feeling that it probably couldn’t have existed even a generation or two ago, and certainly not back when only wood and gut were the available materials.
Tuning in 4ths or 5ths maximizes the number of open strings that fall on simple diatonic scale tones. Any other interval quickly leads to chromatic tones.
Melodic instruments like fiddle family and mando family tend to favor 5ths, which allow a compass of a full octave to be played easily on 2 adjacent strings, but which make close-voicing of chords impossible. Chordal instruments like guitar favor 4ths for the opposite reason, and for less finger stretch on a longer necked instrument.
Guitar vs. fiddle is not really “backwards”. It’s an illusion caused by the fact that 4ths and 5ths are inversions of each other (as octaves and unisons are inversions of themselves). That’s why these intervals are called “perfect” intervals.
The placement of the “short” Major 3rd interval on guitar (G-B) is a historical development. The 6-course tenor lute conceptualized the strings as 3 bass courses and 3 treble courses, separated symmetrically by the 3rd. This is the equivalent of tuning the guitar to E A D F# B E - which is, in fact, used for playing historical lute music. Raising the F# to G moves the 3rd asymmetrically between 4 bass courses and 2 treble courses. This allows for more flexible chord formation at the expense of reducing the treble range - a good trade-off for more harmonically oriented post-Renaissance music.
It’s hard not to talk about music theory, when the answer to the question lies in … music theory. And that’s 223 words - nyah nyah! 
I play mountain dulcimer - everything else is strung “backwards”!!!
from Martin
However if it was playable with a human hand, I think guitar strings could be designed to any tuning - you just adjust thicknesses according to what you want.
from MT Guru
This allows for more flexible chord formation at the expense of reducing the treble range - a good trade-off for more harmonically oriented post-Renaissance music.
I agree wholeheartedly. The left hand is also aided a bunch for playing scales and the power of the right hand thumb to pick bass lines is available in the standard tuning. 
Dennis
They can do it any time. There’s nothing graven in stone about guitar string weights, as any citternist will tell you. If you buy the right weights or use a string tension calculator, you can string anything with any string of any pitch.
The only places I’ve seen trouble are in instruments like tenor guitars & banjos, which were intended to have fairly loose, floppy banjo strings in cgda and which are now often restrung with with taut high-tension strings in GDAE to play irish music. The issue then isn’t the pitch, it’s the different tension intention.
Thanks for all your answers.
Here’s my simple answer, which may already have been stated above
(I hate reading stuff). Fiddles and mandos are small enough that you
can assign each finger to 2 frets without too much of a stretch. The
guitar’s frets are big enough to make that pretty tough so we generally
stick with one finger per fret. So, on a mandolin, you can cover 6 frets
with 3 fingers, then the 7th fret is the same as the next string. This
means you’re tuned in fifths (D is a fifth above G, A is a fifth above D,
E is a fifth above A).
But on a guitar you can only go up 4 frets (corresponding to 4 fingers,
and 4 half-steps), then you have to change strings (or grow more
fingers [or, you know, develop a better reach]). This means you’re
tuned in fourths (A is a fourth above E, D is a fourth above A, etc.)