This dissertation identifies a group of symphonies in which a structured play of major and minor significantly shapes each work. Haydn's preference for basing bimodality in parallel keys (e.g. C, c) not only reveals a close kinship of this repertoire to the da chiesa symphonies, but it also dramatically expands the available harmonic resources of the composition, which now has harmonies belonging to two distinct regions at its disposal. The employment of distant harmonies in musical passages introduces chromaticism and new harmonic relationships that often replace traditional functions. Bimodality thus introduces a strong element of innovation that, in the characteristic manner it assumes in each of the works under study, gives rise to each symphony's unique tone.

Haydn's bimodal symphonies include I:4, I:17, I:26, I:34, I:37, I:45, I:46, I:70, I:78, I:80, I:83, I:95, and I:99. Past critiques, which were grounded in Romantic aesthetics, disparaged the apparent modal inconsistency of bimodal symphonies, mistaking the radical originality expressed here for servile subjection to given norms of taste (e.g. I:95). Recourse to the phenomenological and hermeneutical philosophy of Gadamer, Ricoeur, and Savage, more than offering adequate means for a diffusion of this critique, lays the groundwork for a productive understanding of the repertoire. The play of modes in these works exemplifies the ontological foundation of the artwork in play and the unique mood configured by the work as an expression of the work's mimetic character.

I:3, I:11, I:12, I:18, I:44, I:62, and I:63 serve to illustrate different degrees of modal play, from integrated usage within a major or minor key to the structuring principle of a work, and thus to indicate the place of bimodality within the symphonic tradition as manifest in Haydn's oeuvre. Modal play assumes discernable patterns—enclosure of one mode by the other, deliberate contrasting of modes, emergence, emphasis of progress from one to the other, and a polysemic coincidence of functions—in individual works that remain strikingly original.