A distinct feature of Brahms's compositional style is the cumulative development of melodic material that occurs throughout the composition. This motivic treatment appears in rhythmic and pitch fragments that are prolonged though various repetitions and newly derived figures related to earlier statements at the beginning of the composition. The compositional practices of Brahms as they relate to thematic unity reflect an earlier concept of the Grundgestalt, described in elements of nature by the 19th century philosopher, Johann Wolfgang von Goethe. The creative application of this concept by Brahms influenced the work of Arnold Schoenberg, who provided a more formal description as it relates to music and the compositional process. In this thesis, a relationship between Schoenberg's concept of the Grundgestalt and Brahms's compositional technique of motivic manipulations is explored. Movements from the First and Second Sonata for Clarinet and Piano by Brahms have been selected in order to observe his motivic treatment and the ways in which it permeates the composition. The motivic development that characterizes Brahms's style involves an initial motive with a distinct contour and intervallic content. The motive is manipulated with various techniques such as inversion, rhythmic variety and reordered segments that later transform into newly derived forms. An analysis of motivic material and the techniques that create a type of "developing variation" will be a significant focus of this thesis.