the octave. This sequence of fifths shall be used in the discussions of chord progressions, below. Power chord The perfect-fifth interval is called a power chord by guitarists, who play them especially in blues and rock music. The Who's guitarist, Peter Townshend, performed power chords with a theatrical windmill-strum. Power chords are often played with the notes repeated in higher octaves. Although established, the term "power chord" is inconsistent with the usual definition of a chord in musical theory, which requires three (or more) distinct notes in each chord. Chords in music theory A brief overview The musical theory of chords is reviewed, to provide terminology for a discussion of guitar chords. Three kinds of chords, which are emphasized in introductions to guitar-playing, are discussed. These basic chords arise in chord-triples that are conventional in Western music, triples that are called three-chord progressions. After each type of chord is introduced, its role in three-chord progressions is noted. Intermediate discussions of chords derive both chords and their progressions simultaneously from the harmonization of scales. The basic guitar-chords can be constructed by "stacking thirds", that is, by concatenating two or three third-intervals, where all of the lowest notes come from the scale. Triads Major Both major and minor chords are examples of musical triads, which contain three distinct notes. Triads are often introduced as an ordered triplet: the root; the third, which is above the root by either a major third (for a major chord) or a minor third (for a minor chord); the fifth, which is a perfect fifth above the root; consequently, the fifth is a third above the third—either a minor third above a major third or a major third above a minor third. The major triad has a root, a major third, and a fifth. (The major chord's major-third interval is replaced by a minor-third interval in the minor chord, which shall be discussed in the next subsection.) For example, a C-major triad consists of the (root, third, fifth)-notes (C, E, G). The three notes of a major triad have been introduced as an ordered triplet, namely (root, third, fifth), where the major third is four semitones above the root and where the perfect fifth is seven semitones above the root. This type of triad is in closed position. Triads are quite commonly played in open position: For example, the C-major triad is often played with the third