Retrograde inversion
Retrograde inversion is a fundamental transformation in twelve-tone serial music, where the intervals of a prime tone row are inverted—meaning each ascending interval becomes descending and vice versa—and the resulting sequence is then reversed in order, or equivalently, the prime row is first reversed and then inverted.[1] This operation produces one of the four basic row forms (alongside the prime, inversion, and retrograde) that composers manipulate to generate all twelve pitch classes without repetition, ensuring structural unity in atonal compositions.[2] Developed as part of the twelve-tone technique pioneered by Arnold Schoenberg in the early 20th century, retrograde inversion allows for systematic variation while preserving the row's intervallic content, often notated as RI followed by a subscript indicating the final pitch class (e.g., RI₀ for the form ending on the tonic pitch).[1] In practice, it is derived mathematically from pitch-class sets, where inversion flips each pitch integer a to $12 - a \mod 12, and retrograde simply reverses the sequence; for example, starting from the set [3, 5, 11], inversion yields [9, 7, 1], and retrograde inversion then gives [1, 7, 9].[3] This transformation, combined with transposition, expands a single row into 48 distinct forms, forming the basis of serial composition in works by Schoenberg, Anton Webern, and Alban Berg.[2] Beyond its technical role, retrograde inversion contributes to the perceptual symmetry and coherence in serial music, as it mirrors the prime row in both direction and interval structure, enabling composers to create palindromic or balanced phrases.[1] It is typically analyzed using tools like the tone row matrix, where RI forms appear as columns read from bottom to top, facilitating the identification of row properties such as all-interval series or hexachordal combinatoriality.[2] While integral to strict dodecaphony, the concept has influenced broader post-tonal practices, including integral serialism by composers like Pierre Boulez, who extended it to durations and dynamics.[3]Fundamentals
Definition
Retrograde inversion is a musical transformation that combines two fundamental operations applied to a sequence of pitches or pitch classes: retrograde, which reverses the order of the sequence while preserving the pitches, and inversion, which flips the direction of each interval (upward intervals become downward, and vice versa) relative to the starting pitch. This results in a new sequence that is both reordered and directionally mirrored, serving as a key technique in atonal and serial music for generating varied yet related pitch structures.[1][2] Unlike a simple retrograde, which merely plays the sequence in reverse, or an inversion, which mirrors intervals without reordering, retrograde inversion integrates both processes to produce a distinct form of pitch organization that maintains structural relationships while altering perceptual contour.[3] For illustration, consider a basic four-note pitch-class series: C (0), E (4), G (7), B (11). The inversion form is C (0), A♭ (8), F (5), C♯ (1), obtained by negating the original intervals (+4, +3, +4 semitones) from the starting pitch. Reversing this yields the retrograde inversion: C♯ (1), F (5), A♭ (8), C (0), demonstrating the combined transformation under octave equivalence. In twelve-tone serialism, retrograde inversion constitutes one of the four basic row forms—prime, retrograde, inversion, and retrograde inversion—enabling composers to derive multiple variants from a single tone row for thematic development.[1]Relation to Other Transformations
In twelve-tone serialism, retrograde inversion (RI) belongs to a family of four fundamental transformations applied to a tone row: the prime form (P), retrograde (R), inversion (I), and retrograde inversion (RI). These operations enable composers to generate related variants of the row while preserving its pitch-class set and the multiset of consecutive interval sizes.[1] The retrograde (R) reverses the pitch order of the prime form without changing the sizes of the intervals between consecutive pitches, resulting in a backward traversal that flips the direction of each interval and reverses their sequence. In comparison, the inversion (I) preserves the pitch order but inverts the direction of each interval—turning ascending motions descending and vice versa—while keeping interval sizes and their succession intact, thereby altering the melodic contour without reversal.[1] Retrograde inversion (RI), also known as the inverse retrograde, combines these effects by applying reversal to the inversion (or inversion to the retrograde), yielding a form where both order and interval directions are transformed simultaneously.[2] The interrelations among these forms can be summarized as follows:| Form | Abbreviation | Key Transformation from Prime | Typical Transposition Reference |
|---|---|---|---|
| Prime | P | Original pitch sequence | First pitch |
| Retrograde | R | Reversal of pitch order; directions flipped | Last pitch |
| Inversion | I | Interval directions inverted; order preserved | First pitch |
| Retrograde Inversion | RI | Reversal of inverted order; both effects | Last pitch |
Derivation and Construction
Steps to Derive Retrograde Inversion
To derive the retrograde inversion (RI) of a twelve-tone series, begin with the prime form (P), which serves as the foundational row consisting of all twelve pitch classes in a specific order.[1] The four basic row forms—prime (P), retrograde (R), inversion (I), and retrograde inversion (RI)—are generated from this starting point through interval transformations and reversals.[4] The process involves three sequential steps, relying on semitone interval measurements within the modular 12 pitch-class system, where pitch classes are numbered 0 to 11 and equivalents wrap around (e.g., -1 mod 12 = 11).[5]- Identify the prime form (P): Select the original series as the starting point. For example, consider a simple three-note segment for illustration: P = [0, 2, 4], representing pitch classes such as C (0), D (2), and E (4). The full twelve-tone row would extend this principle to all twelve unique pitch classes without repetition.[1]
- Derive the inversion (I): Reverse the direction of each interval in the prime form while preserving their magnitudes, measured in semitones. An ascending interval of +n semitones becomes descending -n semitones (or equivalently + (12 - n) mod 12 to maintain positive values if preferred). Starting from the first pitch class of P (typically normalized to 0 for calculation), accumulate these inverted intervals. For the example P = [0, 2, 4], the intervals are +2 (from 0 to 2) and +2 (from 2 to 4). Inverting yields -2 and -2: begin at 0, subtract 2 to reach 10 (0 - 2 mod 12 = 10), then subtract 2 again to reach 8 (10 - 2 mod 12 = 8). Thus, I = [0, 10, 8]. This step ensures the inverted form mirrors the prime's contour but flips its directional profile.[4][5]
- Reverse the inverted series to obtain RI: Take the order of pitches in the inversion and reverse it entirely, without altering the pitch classes themselves. For the example I = [0, 10, 8], reversing yields RI = [8, 10, 0]. This combines the mirror-image intervals of inversion with the backward sequencing of retrograde. The resulting RI form can be transposed if needed, but the core derivation remains tied to the original P.[1][4]