(E) and fifth (G) an octave higher, respectively sixteen and nineteen semitones above the root. Another variation of the major triad changes the order of the notes: For example, the C-major triad is often played as (C,G,E), where (C,G) is a perfect fifth and E is raised an octave above the perfect third (C,E). Alternative orderings of the notes in a triad are discussed below (in the discussions of chord inversions and drop-2 chords). In popular music, a subset of triads is emphasized—those with notes from the three major-keys (C, G, D), which also contain the notes of their relative minor keys (Am, Em, Bm). Progressions The major chords are highlighted by the three-chord theory of chord progressions, which describes the three-chord song that is archetypal in popular music. When played sequentially (in any order), the chords from a three-chord progression sound harmonious ("good together"). The most basic three-chord progressions of Western harmony have only major chords. In each key, three chords are designated with the Roman numerals (of musical notation): The tonic (I), the subdominant (IV), and the dominant (V). While the chords of each three-chord progression are numbered (I, IV, and V), they appear in other orders. In the 1950s the I–IV–V chord progression was used in "Hound Dog" (Elvis Presley) and in "Chantilly Lace" (The Big Bopper). Major-chord progressions are constructed in the harmonization of major scales in triads. For example, stacking the C-major scale with thirds creates a chord progression, which is traditionally enumerated with the Roman numerals I, ii, iii, IV, V, vi, vii; its sub-progression C–F–G (I–IV–V) is used in popular music, as already discussed. Further chords are constructed by stacking additional thirds. Stacking the dominant major-triad with a minor third creates the dominant seventh chord, which shall be discussed after minor chords. Minor A minor chord has the root and the fifth of the corresponding major chord, but its first interval is a minor third rather than a major third: Minor chords arise in the harmonization of the major scale in thirds, which was already discussed: The minor chords have the degree positions ii, iii, and vi. Minor chords arise as the tonic notes of minor keys that share the same key signature with major keys. From the major key's I–ii–iii–IV–V–vi–vii progression, the "secondary" (minor) triads ii–iii–vi appear in the relative minor key's corresponding chord progression as i–iv–v (or i–iv–V or i–iv–V7): For