iThis paper proposes a new analytical tool to analyze sonata form in late twentieth-century repertoire: the secondary-parameter network examines musical aspects such as tempo, rhythm, dynamic level, and texture to determine formal boundaries. This method builds on those proposed by Duane (2017), Howland (2015), and Wennerstrom (1975) that allow secondary parameters to be the primary criteria that define form, and it complements many previous definitions of sonata form that rely on either theme or tonal area (Lofthouse 2016, Tan 2012, and Tarrant 2017, 2019). A significant number of secondary parameters change at every formal junction. The secondary-parameter network creates a new perspective of sonata form in which new tendencies arise: "permeable boundaries" occur when sections of two phrases (from different interthematic functions) overlap or alternate so that the next phrase begins before the previous phrase ends. This paper analyzes the first movement of Isang Yun's First Symphony with these concepts.