Scale degree in the context of "Nashville Number System"

In music theory, the tritone is defined as a musical interval spanning three adjacent whole tones (six semitones). For instance, the interval from F up to the B above it (in short, F–B) is a tritone as it can be decomposed into the three adjacent whole tones F–G, G–A, and A–B.

Narrowly defined, each of these whole tones must be a step in the scale, so by this definition, within a diatonic scale there is only one tritone for each octave. For instance, the above-mentioned interval F–B is the only tritone formed from the notes of the C major scale. More broadly, a tritone is also commonly defined as any interval with a width of three whole tones (spanning six semitones in the chromatic scale), regardless of scale degrees. According to this definition, a diatonic scale contains two tritones for each octave. For instance, the above-mentioned C major scale contains the tritones F–B (from F to the B above it, also called augmented fourth) and B–F (from B to the F above it, also called diminished fifth, semidiapente, or semitritonus); the latter is decomposed as a semitone B–C, a whole tone C–D, a whole tone D–E, and a semitone E–F, for a total width of three whole tones, but composed as four steps in the scale. In twelve-equal temperament, the tritone divides the octave exactly in half as 6 of 12 semitones or 600 of 1,200 cents.

In music, function (also harmonic function or tonal function) is a term used to denote the relationship of a chord or a scale degree to a tonal centre. Two main theories of tonal functions exist today:

• The German theory created by Hugo Riemann in his Vereinfachte Harmonielehre of 1893, which soon became an international success (English and Russian translations in 1896, French translation in 1899), and which is the theory of functions properly speaking. Riemann identified three abstract tonal "functions"—tonic, dominant and subdominant—denoted by the letters T, D, and S, respectively, each of which could take on a more or less modified appearance in any chord of the scale. This theory, in several revised forms, remains much in use for the pedagogy of harmony and analysis in German-speaking countries and in Northern and Eastern European countries.
• The Viennese theory, characterized by the use of Roman numerals to denote the chords of the tonal scale, as developed by Simon Sechter, Arnold Schoenberg, Heinrich Schenker, and others, practiced today in Western Europe and the United States. This theory in origin was not explicitly about tonal functions. It considers the relation of the chords to their tonic in the context of harmonic progressions, often following the cycle of fifths. That this actually describes what could be termed the chords' "function" is evident in Schoenberg's Structural Functions of Harmony (1954), a short treatise dealing mainly with harmonic progressions in the context of a general "monotonality".

Both theories find part of their inspiration in the theories of Jean-Philippe Rameau, starting with his Traité d'harmonie (1722). Even if the concept of harmonic function was not so named before 1893, it can be shown to exist, explicitly or implicitly, in many theories of harmony before that date. Early usages of the term in music (not necessarily in the sense implied here, or only vaguely so) include those by Fétis (Traité complet de la théorie et de la pratique de l'harmonie, 1844), Durutte (Esthétique musicale, 1855), and Loquin (Notions élémentaires d'harmonie moderne, 1862).

In music, a primary triad is one of the three triads, or three-note chords built from major or minor thirds, most important in tonal and diatonic music, as opposed to an auxiliary triad or secondary triad.

Each triad found in a diatonic key corresponds to a particular diatonic function. Functional harmony tends to rely heavily on the primary triads: triads built on the tonic, subdominant, and dominant degrees. The roots of these triads begin on the first, fourth, and fifth degrees (respectively) of the diatonic scale, otherwise symbolized: I, IV, and V (again, respectively). Primary triads, "express function clearly and unambiguously." The other triads of the diatonic key include the supertonic, mediant, sub-mediant, and leading-tone, whose roots begin on the second, third, sixth, and seventh degrees (respectively) of the diatonic scale, otherwise symbolized: ii, iii, vi, and vii (again, respectively). They function as auxiliary or supportive triads to the primary triads.

In music or music theory, a thirteenth is the note thirteen scale degrees from the root of a chord and also the interval between the root and the thirteenth. The thirteenth is most commonly major Play or minor Play.

A thirteenth chord is the stacking of six (major or minor) thirds, the last being above the 11th of an eleventh chord. Thus a thirteenth chord is a tertian (built from thirds) chord containing the interval of a thirteenth, and is an extended chord if it includes the ninth and/or the eleventh. "The jazzy thirteenth is a very versatile chord and is used in many genres." Since 13th chords tend to become unclear or confused with other chords when inverted, they are generally found in root position. For example, depending on voicing, a major triad with an added major sixth is usually called a sixth chord Play, because the sixth serves as a substitution for the major seventh, thus considered a chord tone in such context.