tunings allow major triads to be played by barring one fret with only one finger, using the finger like a capo. On guitars without a zeroth fret (after the nut), the intonation of an open note may differ from then note when fretted on other strings; consequently, on some guitars, the sound of an open note may be inferior to that of a fretted note. Unlike the piano, the guitar has the same notes on different strings. Consequently, guitar players often double notes in chord, so increasing the volume of sound. Doubled notes also changes the chordal timbre: Having different "string widths, tensions and tunings, the doubled notes reinforce each other, like the doubled strings of a twelve-string guitar add chorusing and depth". Notes can be doubled at identical pitches or in different octaves. For triadic chords, doubling the third interval, which is either a major third or a minor third, clarifies whether the chord is major or minor. Unlike a piano or the voices of a choir, the guitar (in standard tuning) has difficulty playing the chords as stacks of thirds, which would require the left hand to span too many frets, particularly for dominant seventh chords, as explained below. If in a particular tuning chords cannot be played in closed position, then they often can be played in open position; similarly, if in a particular tuning chords cannot be played in root position, they can often be played in inverted positions. A chord is inverted when the bass note is not the root note. Additional chords can be generated with drop-2 (or drop-3) voicing, which are discussed for standard tuning's implementation of dominant seventh chords (below). When providing harmony in accompanying a melody, guitarists may play chords all-at-once or as arpeggios. Arpeggiation was the traditional method of playing chords for guitarists for example in the time of Mozart. Contemporary guitarists using arpeggios include Johnny Marr of The Smiths. Fundamental chords Standard tuning A six-string guitar has five musical-intervals between its consecutive strings. In standard tuning, the intervals are four perfect fourths and one major third, the comparatively irregular interval for the (G,B) pair. Consequently, standard tuning requires four chord shapes for the major chords. There are separate chord forms for chords having their root note on the third, fourth, fifth, and sixth strings. Of course, a beginner learns guitar by learning notes and chords, and irregularities make learning