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In music, consecutive fifths, or parallel fifths, are progressions in which the interval of a perfect fifth is followed by a ''different'' perfect fifth between the same two musical parts (or voices): for example, from C to D in one part along with G to A in a higher part. Intervening octaves are irrelevant to this aspect of musical grammar; for example, parallel twelfths (i.e., as created by successive intervals of an octave plus a fifth) are equivalent to parallel fifths.〔Thus, the word "parallel" is not truly synonymous with "consecutive" here, as a fifth followed by another fifth approached with contrary motion would still count as consecutive fifths. The term ''parallel fifths'' may therefore be misleading, because some consecutive fifths occur with contrary motion: from a true uncompounded fifth to a twelfth, for example. If parts move by oblique motion (for example, one part moving from a C to a higher C, and another part repeating a G higher than both of those Cs), the intervals are not considered to differ in the relevant way, so parallel fifths do not occur.〕 Though used in, and evocative of, various kinds of popular, folk, and medieval music, parallel motion in perfect consonances (P1, P5, P8) is strictly forbidden in species counterpoint instruction (1725–present)〔 and during the common practice period, consecutive fifths were strongly discouraged. This was primarily due to the notion of voice leading in tonal music, in which, "one of the basic goals...is to maintain the relative independence of the individual parts."〔Kostka & Payne (1995), p.84.〕 A common theory is that the presence of the 3rd harmonic of the harmonic series influenced the creation of the prohibition. ==Development of the prohibition== Singing in consecutive fifths may have originated from the accidental singing of a chant a perfect fifth above (or a perfect fourth below) the proper pitch. Whatever its origin, singing in parallel fifths became commonplace in early organum and conductus styles. Around 1300, Johannes de Grocheo became the first theorist to prohibit the practice. However, parallel fifths were still common in 14th-century music. The early 15th-century composer Leonel Power likewise forbade the motion of "2 acordis perfite of one kynde, as 2 unisouns, 2 5ths, 2 8ths, 2 12ths, 2 15ths," and it is with the transition to Renaissance-style counterpoint that the use of parallel perfect consonances was consistently avoided in practice. The convention dates approximately from 1450.〔 Composers avoided writing consecutive fifths between two independent parts, such as tenor and bass lines. Consecutive fifths were usually considered forbidden, even if disguised (e.g., in a "horn fifth") or broken up by an intervening note (e.g., the third/mediant in a triad). The interval may form part of a chord of any number of notes, and may be set well apart from the rest of the harmony, or finely interwoven in its midst. But the interval was always to be quit by any movement that did not land on another fifth. The prohibition concerning fifths did not just apply to perfect fifths. Some theorists objected also to the progression from a perfect fifth to a diminished fifth in parallel motion; for example the progression from C and G to B and F (B and F forming a diminished fifth). "The reason for avoiding parallel 5ths and 8ves has to do with the nature of counterpoint. The P8 and P5 are the most stable of intervals, and to link two voices through parallel motion at such intervals interferes with their independence much more than would parallel motion at 3rds or 6ths."〔 "Since the octave really represents a repetition of the same tone in a different register, if two or more octaves occur in succession, the result is a reduction in the number of voices; for example, in a two-voice setting, one of the voices would temporarily disappear, and along with it the rationale of the intended two-voice setting. The octave acts merely as a doubling; if, in a particular instance, it is not intended to act as such, this must be sufficiently emphasized by what precedes and follows it. But even the succession of two octaves brings the sense of doubling into the foreground. Of course, this must not be confused with an intentional doubling used to strengthen sonority, for which, however, strict counterpoint offers no motivation."〔Jonas, Oswald (1982). ''Introduction to the Theory of Heinrich Schenker'', p.110. (1934: ''Das Wesen des musikalischen Kunstwerks: Eine Einführung in Die Lehre Heinrich Schenkers''). Trans. John Rothgeb. ISBN 0-582-28227-6.〕 Similarly, "Parallel 8ves...reduce the number of voices...since the voice that () doubles at the 8ve...is not an independent voice but merely a duplication. Parallel 8ves...may also confuse the functions of the voices...If the upper voice succession...is merely a duplication of the bass, then the actual soprano must be...the alto voice. This interpretation of course makes no sense, for it turns the texture inside out."〔Forte, Allen (1979). ''Tonal Harmony in Concept & Practice'', p.50. Third edition. ISBN 0-03-020756-8.〕 "Parallel 5ths are avoided because the 5th, formed by scale degrees 1 and 5, is the primary harmonic interval, the interval that divides the scale and thus defines the key. The direct succession of two 5ths raises doubt concerning the key."〔 The identification and avoidance of perfect fifths in the instruction of counterpoint and harmony help to distinguish the more formal idiom of classical music from popular and folk musics, in which consecutive fifths commonly appear in the form of double tonics and shifts of level. The prohibition of consecutive fifths in European classical music originates not only in the requirement for contrary motion in counterpoint but in a gradual and eventually self-conscious attempt to distance classical music from folk traditions. As Sir Donald Tovey explains in his discussion of Joseph Haydn's Symphony no. 88, "The trio is one of Haydn's finest pieces of rustic dance music, with hurdy-gurdy drones which shift in disregard of the rule forbidding consecutive fifths. The disregard is justified by the fact that the essential objection to consecutive fifths is that they produce the effect of shifting hurdy-gurdy drones."〔Tovey, Donald Francis. ''Essays in musical analysis'', vol. 1, p. 142. Quoted in van der Merwe, Peter (1989). ''Origins of the Popular Style: The Antecedents of Twentieth-Century Popular Music'', p. 210. Oxford: Clarendon Press. ISBN 0-19-316121-4.〕 A more contemporary example would be guitar power chords. In the course of the 19th century consecutive fifths became more common, arising out of new textures and new conceptions of propriety in voice leading generally. They even became a stylistic feature in the work of some composers, notably Chopin; and with the early 20th century and the breakdown of common-practice norms the prohibition became less and less relevant.〔Piston, Walter (1987). ''Harmony'', 5th edition revised DeVoto, Mark, pp. 309–312, 477–480. ISBN 978-0-393-95480-7.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「consecutive fifths」の詳細全文を読む スポンサード リンク
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