The late '60s were a crucial time in the development of minimalist music, with major composers engaging in projects that would profoundly affect their later work. Steve Reich codified his rigorously formalist approach to composition in his seminal essay "Music as a Gradual Process," for example, while Philip Glass was at work developing a particular process of his own—namely his additive/subtractive technique that would come to define his early style. This development is reflected in a number of works from 1968 - 1969, including Two Pages, Music in Fifths, Music in Similar Motion, and the work under consideration here, Music in Contrary Motion. At the core of all of this works is the concept of taking a limited number of pitches and arranging them into short and simple diatonic melodic contours, then subjecting those melodic figures and their constituent motivic segments to repetitive expansions or contractions. The accrual of repeated motivic segments into long melodic strings, and the subsequent dismantling of these extended melodic chains, lends to these works their sense of overall structure. While the other works from the period utilize melodic unison or multiple voices simultaneously moving along the same contours, the sonority of Music in Contrary Motion stands apart in that, as the title suggests, two different melodic strands move in exact mirror images of each other along a horizontal line of symmetry and within a simple diatonic pitch space. All of the pitches fall along a basic A minor scale (that is, it's an "all white key" piece), with the top line starting at an A and extending above it to an E, and the bottom line starting on the E below and extending from there down to the A below. In addition to the symmetry found across the horizontal axis between the two lines, an additional kind of symmetry is built into the initial melodic gestures both parts execute. Both parts traverse their ranges in two ways: by simple scalar stepwise motion and by ascending or descending third leaps alternating with stepwise moves in the opposite direction in a zigzag fashion. A scalar ascent and zigzag descent in the upper voice (and mirrored in the lower) is reflected across a vertical axis of symmetry by recasting the zigzag figure as an ascent, followed by a scalar descent. Because the voices are spaced within the same ranges of different octaves, the symmetry of the figurations thus ties the different lines together in intricate ways. For example, the scalar ascent from A to E in the upper voices is repeated at the octave in the lower voice at the precise moment that it is inverted (as a scalar descent) in the upper voice; a zigzag figure rising through the lower voice continues its trajectory through the upper line. These interconnections become increasingly complex as Glass' additive procedures create an undulating metrical underpinning that leaves the ear lurching forward at the work's abrupt and unexpected conclusion.

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