So... What exactly is the guitar?

The guitar is such a well-known instrument that this seems like a very stupid question. We've all seen one, right? We've all strummed at least a couple of chords on one! But looking closely at any musical instrument will always point out new things to explore by showing us what its possibilities and limitations are.

Explore the anatomy of an acoustic (classical) guitar, in and out

Explore the anatomy of an electric guitar, in and out

Basically, all instruments are composed of three elements (as defined by organology, the branch of musicology that studies musical instruments):

An element that produces the initial vibration
An element that vibrates
An element that resonates with that vibration, thereby amplifying it so it can be heard

That is all. And believe me, not a single musical instrument escapes this rule.
Talking of our instrument, the guitar, we have:

Fingers (with or without long nails)/Plectrum (pick)
Strings
Body

Unless, of course, we use an electric guitar, in which case no.3 changes into a slightly more complex system, involving a transducer (pick-ups), an amplifier, and a speaker. Or a semi-acoustic guitar, in which case we get a combination of both.

But this -without considering electric guitars- might be an adequate description of even a (seemingly) very primitive instrument, with only 1 string, no fretboard, and a dried pumpkin as its body!

A guitar, however, is a little more complex!

First of all, it is a tempered instrument. Our choice of notes on a guitar is limited to the 12 tones of the chromatic scale, which derives naturally from the circle of fifths.

A violin, in contrast, is a non tempered instrument. On such instruments, the player has an infinite choice of notes. Intonation then becomes a critical point, since it depends wholly on the players ability -and the musical system being used.

There is no point in trying to play Arabic music with thirds of a tone on a guitar, for instance, as the smallest interval at our disposal is a semitone. But the violin is ideal for this kind of music.

So, when playing a guitar we are limited to the genres, styles, and traditions that use this 12 tone system as their basis: music from the late baroque period, classical and romantic music, and some XXth and XXIst century music (forget Xenakis, Scelsi, and Carrillo though!).

Some music from the Renaissance can be transcribed for the guitar, although it was composed for instruments that use just intonation, which has a brighter and more melodious quality.

Just Intonation

And of course, we can play blues, jazz, R&B, funk, rock, pop, bossa-nova, salsa, etc, all of which make use of traditional harmony as it was used prior to the explorations of the more radical XXth and XXIst century composers, who have pushed far beyond the limitations of the 12 tone tempered system in many different ways.

Once this is clear, it becomes obvious that fully understanding all the possibilities within the 12 tone tempered system, including the 12 major and 12 minor keys (15 of each, if we take enharmonic keys into account) is the first key point in unlocking the potential of the guitar.

Of course, we could jump into the late XXth century and start producing all kinds of interesting sounds and noises by scratching, tapping, pulling, rubbing, etc. the different elements of our instrument. But we can produce these same sounds with different contraptions.

The essence of the guitar remains within the 12 tone tempered system, and the pentatonic structure on which the tuning of the strings is based.