Why is there that funny tuning kink between the G and B string on a guitar in standard tuning? I.E. the gap (interval) between the rest of the adjoining strings is 5 frets (semitones) (or a perfect fourth), but the gap between the G and B string is only 4 frets (semitones) (or a major third). Why is that?
It seems to make more sense to tune it all in perfect fourths and end up with EADGCF. I understand that other string instruments have the same gap between all of their strings.
I've seen it argued that the instrument that became the guitar started with the major G chord set, the second, third and fourth string, probably in pairs, as the entire string set for the instrument. The first string was then added, and the lower strings were added in fourths to provide more bass harmony, much the same way we see the 7th string being brought in these days.
Man, I wish I could source that.
In a more practical manner, I play mandolin, which is tuned in fifths. For melodies, it makes great sense to tune in fifths. Scales that seem kinda haphazard on guitar just lay out so nicely on the mandolin. But chords are ugly hand-stretchers. David Grisman, a great bluegrass and newgrass mandolin player, suggests that if you have to play four-or-more-note chords, drop the root and let someone else play it. Guitars, being tuned mostly in fourths, make chords much easier.
Actually there is an alternative. There are a few guitarists who tune their entire guitar in "straight fourths", such as
E A D G C F
There is an article on All Fourths tuning on Wikipedia.
Stanley Jordan is a famous jazz guitarist who uses this tuning exclusively.
Freddie Green, the famous rhythm guitarist with the Count Basie orchestra, effectively played only in all-fourths tuning by virtue of the fact that he only played on the bottom four strings of the guitar, moving up and down the neck a great deal, but virtualy never crossing over that major third to the high B and E strings.
Also the Chapman Stick, a unique 10-course instrument related to the electric guitar, uses straight fourths for the top five strings and fifths for the lowest five strings.
When I studied jazz guitar, I determined to teach myself to play in straight fourths. I believe it has many advantages. The more complex the chords and harmonic progressions you are playing, the more the straight fourths system makes sense.
But if you want to learn music by exactly copying your favorite solos and pieces transcribed from famous guitarists, you're going to need to use the same tunings that those guitarists used.
I was under the impression it was more historical than anything else, although Wikipedia tells me:
I think it's tuned like it is to maximize the number of strings we can use in chord voicings.
If the guitar were tuned in fourths, barre chords would be out.
The tuning EADGBE makes certain important technical things possible on a six string guitar.
In a symmetrical tuning like EADGCF the top two strings (top and bottom refer to pitch, not location on the guitar) are outside the keys of E, A and D major. Solo guitar music depends heavily on the use of open strings- with an open string in the bass, the left hand is free to move all over the fretboard. If you have E in the bass, the first string F open is not convenient, neither is C. It makes more sense for an E in the first string and the perfect fifth on the second. Not only are they in E major but they are also in E minor, A major, A minor, D major and D Dorian and C major, G major etc.
Conversely, if you play in the key of F in standard tuning, there is no open string and one finger is anchored to that note, limiting the movement of the left hand. Solo music becomes much more difficult and limited in this key. This is also why solo guitar music tends to favor sharp keys- when we proceed through the flat keys we start losing open strings immediately in F major, Bb, Eb etc. In many cases it would be better to retune the entire guitar flat for pieces that require these keys in an ensemble setting.
With the fifth and the octave on the first two strings, barre chords become possible with one finger and other chord tones fall under the fingers well. In a symmetrical tuning we do not have enough fingers to play a full E major chord even in open position. It makes more sense to shift one fret for single note runs than deal with chords in a difficult, limiting way.
The use of fourths separating the bass strings is also important from a technical standpoint. If you have only a low E string and wish to play the three primary notes in the key of E, (E, A and B) you must move up the string to the fifth fret to find the A. This is a long distance which is not a problem when playing an open string, but when playing in a key like F or G you must fret a note and then move that long distance or stretch. The next A string puts the subdominant A very close to E and B is just a whole step higher than A. A small two fret box containing the primary notes then repeats up the neck making those three notes easily accessible for all keys, major or minor.
If the next string is B instead of A, then the B is convenient but the A requires moving a long distance up the string. Of course standard tuning doesn't fit the needs of every piece of music you might play- so we retune certain strings or use capos or retune the entire guitar as needed.
I should also make reference to the practice of tuning the guitar in 5ths. "Crafty" tuning, or "New Standard Tuning", popularized by guitarist Robert Fripp of the rock band King Crimson, is based on this principle.
In Crafty tuning, the lowest note on the guitar is the "C" below the usual low "E", as on the cello, and the strings go up in 5ths from there, except for the highest string. Special string gauges are required to get this to work correctly.
There was an active guitar education movement called Guitar Craft built around the "Crafty" system some years ago.
In Bill Edwards, Freboard Logic books, I remember him explaining that the interval mix of EADGBE is pretty optimal if the goal is to find a compromise between easy scales and easy chords.
That little kink is essential if you're trying to play slide in standard tuning. If you play slide on EADGCF, you can't make any chords!
For folk guitar (with/or without a slide), it's often useful to make it a curve by dropping the E to D. It makes possible the stacked-thirds that piano players (and horn sections) are so proud of. And that minor third on top makes slide playing really fun.
With all due respect I would not call it a kink, or quirk.
The tuning of the guitar as is creates optimal opportunities for fingering of the chords and chord melodies that are frequently played on guitar. It may be somewhat historical but that doesn't mean it isn't functional. Things evolve to meet a need.
Today's guitarist is frequently more concerned with playing single note lines as fast as possible. Any alteration of the guitar that helps one achieve this goal is an "evolution". Historically the guitar was used as a multi voice instrument both in group setting and solo. Solo classical guitarists play all voices, Bass line, rhythm accompaniment, and melody or solo lines.
There are plenty of alternate tunings for the guitar but in my experience the standard tuning makes standard chord progressions very sensible and logical in terms of movement and ease of play while fingering melody notes on the top strings.
As a specific example, for the minor ii - V - i chord progression (E-7(b5) --> A7 --> D-7) All three of these chords have the exact same fingering (different inversions) at the 5th fret each covering four strings.
I've heard a lot of modern guitarists complain that they can't play a major bar chord starting on the D string because of the B string. In my opinion this is not a good reason to pick a tuning as you will not encounter consecutive major chords in 4ths in any key signature. The same analysis works for other common progressions.
To this end I might say that the choice of tuning should make your choice of musical playing style sensible. So tuning in all fourth might make sense for some tasks, open tuning makes sense for others. But I think standard tuning covers more bases. As I stated in the beginning things evolve for a reason. If the reason goes away, the need goes away, and it's time for more evolution.
Just a bit of an addition to all the excellent answers so far ...
The renaissance lute has a very similar tuning system, although the "kink" in the tuning is between a different pair of strings (or "courses" of double strings, usually). Standard guitar tuning can be converted to renaissance lute tuning by two simple steps: tune the g string down to f-sharp, and put a capot on at the third fret.
So, it would seem that the presence of the "kink" in the tuning goes back a long way before the modern day guitar tuning.
To add to @OldJohn's answer, renaissance viols also followed this "kinked" tuning pattern, e.g. D G C E A D (6 strings) or A D G C E A D (7 strings).
Clearly this tuning meme was applied to a range of different types of fretted instruments. One possible explanation is that it helped to accommodate them to non-equal temperaments, using "unequally" spaced frets. For example tuning a 7-string instrument in fourths, A D G C F Bb Eb, the first fret would either give A# D# G# C# F# B E or Bb Eb Ab Db Gb Cb Fb. Either you have a clash between A#/Bb and D#/Eb on the outer strings if an group (consort) of viols are playing together, or the flats and dbuble-flats go way outside the conventional key range of the period.
That said, some music for viols was apparently intended to be played in (an approximation to) equal temperament, but that may have been "avant garde experimentation" compared with the customary unequal tuning. Unlike modern guitars, the frets on both lutes and viols were adjustable, being simply loops of gut tied around the neck of the instrument.
Why is the guitar tuned like that?
Short answer: tune your guitar in 4ths EADgcf and strum your EMaj chord. Can't hear it? Play your E and f strings together. That's why we don't tune it in 4ths.
Why B instead of C? Look at your cycle of 5ths/4ths with E as the I note. You'll see A is the V and B is the IV
