The previously discussed I-IV-V chord progressions of major triads is a subsequence of the circle progression, which ascends by perfect fourths and descends by perfect fifths: Perfect fifths and perfect fourths are inverse intervals, because one reaches the same pitch class by either ascending by a perfect fourth (five semitones) or descending by a perfect fifth (seven semitones). For example, the jazz standard Autumn Leaves contains the iv7-VII7-VIM7-iiø7-i circle-of-fifths chord-progression; its sevenths occur in the tertian harmonization in sevenths of the minor scale. Other subsequences of the fifths-circle chord-progression are used in music. In particular, the ii-V-I progression is the most important chord progression in jazz music.
The next step is to figure out what gauge, or thickness of string is best suited to your playing ability and style. Thinner gauges are easier to fret and bend, and may be better suited for beginners, until callouses build up on the fingertips. Heavier strings tend to produce greater volume and fuller tone. Nylon strings are typically categorized as light, medium or heavy tension. Steel strings for both electric and acoustic guitars are categorized by the gauge, or thickness of the lightest string, the high E string, measured in thousandths of an inch, with .09 being a common size for an electric set. A set of electric strings may be labeled .09-.042 - this is the gauge of the lightest and heaviest string in the set. Acoustic sets are a little thicker, so a typical medium-gauge set might be .012-.054.
With so many options available in the world today, buying a guitar that perfectly represents your own style, tastes, and attitude has never been easier. Whether you're a classical guitarist looking for that perfectly balanced nylon flamenco, or a hard rock enthusiast who needs Pete Townshend crunch combined with Jack White power, there is simply no shortage of axes to choose from.
As previously stated, a dominant seventh is a four-note chord combining a major chord and a minor seventh. For example, the C7 dominant seventh chord adds B♭ to the C-major chord (C,E,G). The naive chord (C,E,G,B♭) spans six frets from fret 3 to fret 8; such seventh chords "contain some pretty serious stretches in the left hand". An illustration shows a naive C7 chord, which would be extremely difficult to play, besides the open-position C7 chord that is conventional in standard tuning. The standard-tuning implementation of a C7 chord is a second-inversion C7 drop 2 chord, in which the second-highest note in a second inversion of the C7 chord is lowered by an octave. Drop-two chords are used for sevenths chords besides the major-minor seventh with dominant function, which are discussed in the section on intermediate chords, below. Drop-two chords are used particularly in jazz guitar. Drop-two second-inversions are examples of openly voiced chords, which are typical of standard tuning and other popular guitar-tunings.
Guitars have been played since the Renaissance era, after descending from the ancient Greek instrument, the kithara. Or, at least, that's how the theory goes: the only real proof for this is the similarities between the Greek word and the Spanish word, quitarra. Early guitars often had four strings, evolving into the six-string version we know today in the late 1600s. Anton Stradivari, the famous violin-maker, also had a hand in making guitars. There's now only one Stradivarius guitar left in existence.