Reginald Smith Brindle once claimed that “a whole generation [of composers] dedicated their efforts in one way or another to the exploration of the field between tonality and atonality, and to the integration of serialism into a more accessible language.” But how was such integration actually to be achieved? Chapter 1 addresses this question from a music-theoretical perspective. In an attempt to explain how post-tonal harmonic progressions might “make sense,” Smith Brindle himself formulated theories of tension flow and tonal-atonal equilibrium in his 1966 textbook, Serial Composition. The former theory compares the number of consonant and/or dissonant intervals between chords, albeit without providing a consistent means of distinguishing between similar sonorities; the latter observes that various musical passages strike a balance between functional and non-functional harmony, albeit without explaining the nature of said balance (or, indeed, what it is for something to be functional or non-functional). While his ideas are evocative, they lack theoretical finesse. Placing them in dialogue with recent developments in post-tonal scholarship helps to unlock their potential. Joseph Straus’s theory of voice leading in set-class space, for example, defines tension flow more rigorously: coherent post-tonal progressions often move smoothly from an initial, chromatically compact set class to one that is more open and spacious. To my mind, sets of the latter type often resemble traditional seventh chords; they contain a tritone that requires resolution. If this tritone resolves to a third, then a contrapuntal resolution takes place, even if that third is housed in a dissonant harmony. Smith Brindle’s concept of tonal-atonal equilibrium neatly captures this effect—of simultaneous melodic release and increased harmonic tension. I explore the practical implications of these ideas through analysis of The Harmony of Peace from Smith Brindle’s Ten Simple Preludes (1979) and the first fragment of his El Polifemo de oro (1956). I conclude the chapter, however, with an analysis of the latter piece’s third fragment, in which tonal-atonal equilibrium is manifested by non-dodecaphonic means. Rather than clinging to serialism unthinkingly, Smith Brindle uses it as a creative spur to craft his own system and affects.