吉他的空弦音為什麼是現在這6個音？

01-02

吉他的根音為什麼是現在這6個音？是逐步發展過來的么？誰對吉他的發展貢獻最大？
我自己猜測是為了演奏的時候換手指方便。

瀉藥,

C D E F G A么?

未必吧, 以B為根音的G和弦也很常見，

再放開一些考慮離調的話，那就更多了，像{x13231}的bBmaj7以bB為根音，如此種種，不一而足。

經@何無空同學提醒，題主可能想問的是空弦音.

下文非常非常粗糙地翻譯了一下，

為什麼吉他調弦會是這樣的？EADGBE？
人們早在千年以前就發現五度音程聽起來最爽。
但是吉他的調弦比較特別(5-5-5-4-5)。何哉？
「為了儘可能減小左手移動幅度」
「G-B的4個半音可以提供更多編排可能」
總之這種調弦法是便利性和樂理的妥協
以前五弦琴用的是ADGBE，

而吉他在此基礎上，加上比A低5個半音的E音，是16世紀以後的事。

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Fender - The Why and When of Standard Guitar Tuning
Why are guitars tuned EADGBE—a series of perfect fourths and a single major third?
Good question, not least because for the past 1,000 years, most everyone seems to have agreed that the most naturally powerful and pleasing-to-the-ear interval is the mighty perfect fifth. All Western music is pretty much based on the hallowed circle of fifths. Stringed instruments such as the violin, cello and mandolin are tuned in fifths.
And yet there』s the guitar—an extremely popular instrument—tuned in a seemingly odd series of ascending perfect fourths and a single major third. From low to high, standard guitar tuning is EADGBE—three intervals of a fourth (low E to A, A to D and D to G), followed by a major third (G to B), followed by one more fourth (B to the high E).

This arrangement was not arrived at and agreed upon just to confuse everyone. Wikipedia editors and contributors sensibly note that standard guitar tuning 「evolved to provide a good compromise between simple fingering for many chords and the ability to play common scales with minimal left hand movement,」 and that the four pairs of perfect-fourth string intervals produce 「a symmetry and intelligibility to fingering patterns.」 Of the anomalous major third from G to B, it notes that although 「this breaks the fingering pattern of the chromatic scale and thus the symmetry, it eases the playing of some often-used chords and scales, and it provides more diversity in fingering possibilities.」
So there』s our answer: The guitar is tuned the way it usually is because it』s simultaneously musically convenient and physically comfortable.
This, by the way, is an arrangement largely settled on hundreds of years ago. When the five-course (course in this sense meaning a pair of strings tuned in unison) guitarra battente first appeared in Italy in the 1500s and gradually replaced the four-course guitar-like instruments dominant since the beginning of the Renaissance a couple centuries earlier, it was tuned ADGBE, as are the top five strings of the modern guitar (the transition from five pairs of strings to six single strings was under way in Europe by the middle of the 17th century). Tuning the third and second strings (G and B) to a major-third interval made fingering easier than continuing a series of perfect fourths, which would』ve resulted in a second string tuned to C and a first string tuned to F. Lowering what would』ve been that high open F by one half step to an open E returned the interval from first string to second string (B) to a perfect fourth.
Don』t just take Wikipedia』s word for it about the sensibility of the arrangement, though. Noted music instructor and former Television guitarist Richard Lloyd once wrote on his website that while the violin and the cello lend themselves nicely to tuning in fifths because of their small scale length, the same doesn』t necessarily hold true on a larger-scale instrument such as a guitar.
「The guitar is a larger-scaled instrument which is played sitting in one』s lap,」 Lloyd wrote. 「Even though the cello is a larger instrument than the violin, it is played with the neck vertically, which allows the hand to have a little bit easier time reaching for notes. With the guitar sitting in the lap and the neck diagonal to the player, the bend in the wrist starts to make it more difficult to spread out the fingers. So our next best choice for tuning any larger scaled multi-stringed instrument is going to be to tune in fourths, which are a little closer together. On a guitar, a person with a normal-sized hand can reasonably be expected to sound the major third with the pinkie finger while holding down the tonic with the index finger. So it makes sense that the next string should be the fourth.」

Lloyd also astutely noted, however, that if six-string guitars were tuned completely in perfect fourths, you』d wind up with a harmonically discordant arrangement of (low to high) EADGCF. You can see the problem there—E and F are only a half step apart, imposing a naturally irritating interval of a minor second. 「This is a god-awful interval,」 Lloyd wrote. 「And threatens to sour the whole thing.」
Fortunately, since the ADGBE tuning for the top five strings had already been adopted in the 16th century—before a lower sixth string tuned to E was added—such a problematic tuning arrangement was avoided. That lower E continued the arrangement of perfect fourths used for all string pairs except the major-third interval adopted for the second and third strings, resulting in the standard guitar tuning that remains today.

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對了，根據Guitar Pro 6,

七弦琴的標準調弦仍然是E減5個半音，BEADGBE.

八弦琴的標準調弦仍然是B減5個半音，bGBEADGBE.

方便演奏……就這麼簡單

定弦方式很多的，不止是 EADGBe，各種亂七八糟的定弦多了。比如有人說了Drop D，就是為了方便使用一根手指在 4 5 6 弦上彈 Power Chord。還有彈滑棒吉他的也會使用特殊定弦，是為了方便用滑棒演奏和弦。

標準定弦是綜合考慮了手指延伸能力和和弦演奏的方便性下決定的。這種定弦方式基本上都是相差純四度（某一組除外）。

如上兩位層主所說，為了儘可能減小左手移動幅度以及在樂理上方便於演奏和弦，乃至被統一使用了一段時間後樂手們普遍形成了習慣。

而這種調法的確是可以因演奏方便而改變的，參見《和弦進行活用與演奏》

調音方式很靈活，比較普遍的是EADGBE，主要是為了方便演奏，沒有定式

你說的那是空弦音，不叫「根音」。學學樂理吧，這樣萬一有人有閑心回答你時，至少你能看懂。

EADGBE 只是一種調弦方式，是最常用的，還有別的方式。另外也有7弦吉他。