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In music theory, the concept of root denotes the idea that a chord could be represented and named by one of its notes. It is linked to harmonic thinking, that is, to the idea that vertical aggregates of notes form a single unit, a chord. It is in this sense that one can speak of a "C chord", or a "chord on C", a chord built from C and of which C is the root. The root needs not be the bass note of the chord: the concept of root is linked to that of the inversion of chords, itself deriving from the notion of invertible counterpoint. In tertian harmonic theory, that is in a theory where chords can be considered stacks of thirds (e.g. in common practice tonality), the root of a chord is the note on which the thirds are stacked. For instance, the root of a triad such as C-E-G is C, independently of the order in which the three notes are presented. A triad knows three possible positions, a "root position" with the root in the bass, a first inversion, e.g. E-G-C, and a second inversion, e.g. G-C-E, but the root remains the same in all three cases. Four-note seventh chords know four positions, five-note ninth chords know five positions, etc., but the root position always is that of the stack of thirds, and the root is the lowest note of this stack (see also Factor (chord)). Some theories of common-practice tonal music admit the sixth as a possible interval above the root and consider in some cases that chords nevertheless are in root position – this is the case particularly in Riemannian theory. The concept of root has been extended for the description of intervals of two notes: the interval can either be analyzed as formed from stacked thirds (with the inner notes missing): third, fifth, seventh, etc., (i.e., intervals corresponding to odd numerals), and its low note considered as the root; or as an inversion of the same: second (inversion of a seventh), fourth (inversion of a fifth), sixth (inversion of a third), etc., (intervals corresponding to even numerals) in which cases the upper note is the root. See Interval. Chords that cannot be reduced to stacked thirds (e.g. chords of stacked fourths) are not amenable to the concept of root. A major scale contains seven unique pitch classes, each of which might serve as the root of a chord: == Identifying a chord's root == Although the safest way to recognize a chord’s root is, after having reduced the chord to close spacing, to rearrange it as a stack of thirds, there are shortcuts to this: in inverted triads, the root is directly above the interval of a fourth, in inverted sevenths, it is directly above the interval of a second.〔Wyatt and Schroeder (2002). ''Hal Leonard Pocket Music Theory'', p.80. ISBN 0-634-04771-X.〕 Various devices have been imagined to notate inverted chords and their roots: *Chord names and symbols *Roman numeral analysis *Slash chords *Etc. Chords in atonal music are often of indeterminate root, as are equal-interval chords and mixed-interval chords; such chords are often best characterized by their interval content.〔Reisberg, Horace (1975). "The Vertical Dimension in Twentieth-Century Music", ''Aspects of Twentieth-Century Music'', p.362-72. Wittlich, Gary (ed.). Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0-13-049346-5.〕 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「Root (chord)」の詳細全文を読む スポンサード リンク
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