From the mid nineteenth century onwards, musical form has primarily been defined in terms of predetermined paradigms, which ostensibly provide a framework for hierarchically ordered materials. Despite its pervasive presence in theoretical literature, however, this Formenlehre tradition is not universal in musical thought. Since antiquity, theorists have resorted to images of dynamism, change, process, energy, intensity, and narration to denote a more elastic conception of (musical) form. However, most of them – such as, for instance, Kurth, Asaf’yev, or Maus – have not recognised that it is ultimately performers – not composers – who individually shape musical materials on the basis of the structural relations that they perceive within the music and then project in performance. This dissertation explores how such apparent incompatibility between theory and practice might be bridged. To that aim, the first part discusses how ‘dynamic’ notions of musical form might realise their full explanatory potential by accounting for the reality of performance. It also reviews previous investigations of performers’ strategies to project their structural understandings of musical works, with a special focus on their handling of timing, dynamics, articulation, intonation, and timbre. Using recorded interpretations of Brahms’s Cello Sonatas as sources for three case studies, the second part evaluates dynamic ideas of musical form from an analytical viewpoint. Through their personal approaches to these works, I show how select performers create a wide range of structural connections, which are never alike across their different recordings. Likewise, these performers neither resort to the same parameters nor ‘shape’ the select movements in the same manner or with the same intensity. I ultimately posit that musical structure is inferred, created, and experienced in a unique way on every occasion a given piece is performed – and also whenever it is composed, analysed, or listened to. This research does not dismiss music theory as having no explanatory potential in the investigation of abstract notions such as musical structure as we sense them in performance. Rather, it aims to contribute to the dialogue between theory and practice by showing how, and why, music theory should reconceptualise musical form as a set of possibilities affording multiple choices and interpretations, that is to say, as a ‘multiverse’ that emerges across time and in sound.