One of the reasons why so many people take up the guitar as a musical instrument is because of the fact that it is one of the few instruments that can be played entirely on its own, providing both the main tune and the background chords. Having said that, there is a wide range of extra accessories that can be used in conjunction with the guitar, either for holding it in place, or for actually playing it. One of these is commonly referred to as a capo, although its full name is the capotasto.
A capo is a bar that can be clipped to the fret board of a guitar, and pinches the strings against the fret at a point which directly lowers the pitch of the strings, and thus the guitar as a whole. In order to lower the pitch of a guitar by the equivalent of one semitone, the capo would be clipped against the strings just beneath the first lower most fret.
The main reason that guitarists use a capo to change the pitch in this way is so that they can play sheet music that is scored in different keys without having to change the way in which the chords are played, since chord formations are different depending upon the key being played. By simply increasing the pitch of the guitar, the instrument can be played in a range of keys whilst still allowing the guitarist to use the same familiar chord patterns.
As a result of this, it is often used by beginners, although many purists refer to the use of a capo as cheating, and actually refer to capos as cheaters. There is a second reason why a capo may be used however, and that is to increase the pitch in such a way that they match the pitch of those instruments that were used to perform music written a long time ago, such as the renaissance lute.
Another often used accessory is a slide, frequently used in country music, and blues, to create a Hawaiian effect to the sound, although the more accurate name for the sound is glissando. In country music the slide originated by players using the neck of a bottle, and some performers still use these today.
Modern slides tend to be made from a variety of materials, depending upon the effect that the performer wants to achieve. Common materials include glass, metals such as steel or brass, ceramic and plastic, and these vary significantly in weight, which in turn affects the tone of the music. Steel guitars have a slide built in to them as they are used to perform music in this style, and in some cases a Dobro guitar is used, which achieves the same effect.
Perhaps the most commonly used and known accessory for use in playing a guitar however is the plectrum, or pick. A plectrum is a very small, flat piece of material which is used to strum or pick the strings of a guitar in a more exact fashion than using the fingers. Some players grow their own picks, having the nail of one finger kept to a long length, but this is not always desirable or convenient for most players, and a pick that can be used whenever the need arises is a cheap and easy to acquire accessory.
Generally the players that perform with their nails are classical guitarists, and those who use picks or plectrums are performers of electric or acoustic guitars. Plectrums are most commonly found manufactured from plastic, which can be produced in a range of grades, from lightweight and flexible, to a thicker, firmer pick that produces a harder note. Other materials can also be found, including bone, metal - particularly steel, wood, and in some cases, even the shell of a tortoise.