Why not the high E at the top and the low E bottom? I haven't even heard of an alternate tuning that's similar. Is there a reason for this?
There are left handed guitar players who just turn a right stringed guitar over and play that way, so it is possible. With very good results even, see e.g. Albert King:
So it is not unheard of to play that way. Like others have indicated, you need more power for the lower strings, which is suited for the thumb. Plucking chords becomes more difficult with the reverse order too. That is probably some of the reasons why the current order survived.
Try playing something complex on the top (thin) string. Now try the same on the fat string. The fretting hand is more comfortable not being stretched. I suppose more intricate note patterns are traditionally played on the high strings, whereas the E and A would be used for more static bass-like patterns. It gives a slight advantage to the player the way it is.Chord fingerings may also be slightly easier, particularly the 'open'type chords which acoustic players prefer, as they're often played on the 'top' strings, rather tan 'bottom', which would involve arching the fretting hand more.
Also, as with a lot of things, once the trend was thus, it was easier to perpetuate it. Think of right-hand screw threads, and probably hundreds more examples - driving on a particular side of the road.
Look forward to many interesting answers.
Having said all of that, I play with a bass player who is left handed, and he uses 4-string, 5-string and 8- string basses, all of which are strung for right-hand playing. Since he learnt that way, it appears to be no trouble to him.
Looking online, there are plenty of explanations for particular guitar tunings (open, drop etc.), but I haven't found a definitive explanation of why the lowest string is "at the top" and the highest string is "at the bottom", to help reinforce this answer.
Like Tim, I can't wait to see how other people answer this question, particularly as I often tell my guitar pupils that this is the only (!) confusing thing about playing the guitar. (If only…)
However, let me suggest a couple of possibilities. They relate to two main uses of the guitar and its predecessors: playing homophonic (in the case of the guitar, usually strummed) chords; playing melodic and/or contrapuntal music.
When strumming the strings of a guitar, the pick, thumb or fingers strike the bass note of the chord first when playing a downstroke (which, as the hand is falling, tends to be a stronger stroke). This gives particular emphasis to the bass note, upon which the resonance and harmonic character of the chord is built. In relation to this, when one arpeggiates a chord by playing a downstroke (which is arguably the most natural stroke), the harmony-defining bass note is heard first; this is also the natural way to arpeggiate on a number of other instruments (piano and harp, for example).
It is also worth noting, that using the thumb for bass notes (which this ordering of strings allows) has benefits in terms of chord voicings too, whether playing contrapuntal music or playing non-strummed chords (i.e. when each finger and the thumb play one note each). In these cases, the fingers can play notes on adjacent strings easily, as they are close together, and the thumb can easily play strings further away from the strings played by the fingers; and this is conventionally the most resonant way to space a chord, with larger spaces between notes at the bottom, than at the top.
When playing contrapuntal music (music with at least two independent melodic lines), one would often expect the lower, bass line to progress in slower note values (partly because of the harmonic function it serves, but also because lower pitches "speak" more slowly), and the higher line to progress in quicker note values. The "single" right-hand thumb is better suited to this bass role, while using two or more right-hand fingers allow faster articulation of higher melodic lines. Certainly, from a classical guitarist's perspective, this more than any other reason explains why the strings are ordered high-to-low in this direction.
But, this doesn't, of course, explain why so many other string instruments also have their strings ordered in the same direction. The techniques, particularly when using a bow, and horizontal/vertical playing positions of these other string instruments, have little or no relation to my reasoning above; and it does seem unlikely that the playing techniques and construction norms for so many string instruments developed entirely independently…
Because you're looking at it wrong? Guitars are typically strung with the BASS/LOW strings ON TOP. That is - the guitar is typically held with those strings at a higher altitude, closer the player's head. This is only convention and it has very little practical reason and there are plenty of people who play it "upside-down" or string a guitar upside-down and play left-handed. With the exception of some minor tuning issues which can usually be fixed, there is nothing wrong with that.
Play a barrée. Now try fingering something melodic on the high strings, and in comparison, on the low strings.
The typical blues pattern in F consisting of 1-3-1-2-1-1, 1-5-1-2-1-1, 1-6-1-2-1-1 actually does so. But it is rather a stretch and more playable on the flimsier fretboards of electric guitars or in higher positions.
Doing the more melodic stuff on higher strings instead requires less of a hand/finger bend/stretch.
Also if you are playing in the highest positions way off the neck, you'll arguably be doing that for playing high notes. And the traditional string order makes the high sounding strings easier accessible in those positions.