About new stage genres in the music of the second half XX century

New musical and theatrical genres that demonstrate post-non-classical musical thinking are considered. The most common are happening, performance and instrumental theater. Genres are considered differently by V. Petrov, M. Pereverzeva, Yu. Gnirenko and M. Katunyan, but, however, without disclosing their ontology and logical basis. The main distinguishing features of the new stage forms are the openness of the structure, the creative function of the performers and temporal unlimitedness, which indicates the rhizome and rhizome thinking of the composers. It is proposed to consider the new musical and theatrical realities as non-linear, in particular dissipative, based on a non-linear type of determinism – self-determinism. On its basis, a rational construct is established in the form of self-organization (performer), or performing will, which provide the musical material with the quality of integrity. Alternative musical theater is another form of new musical stage genres that have emerged in the post-non-classical era, or in the post-modern era. It is presented by alternative opera and alternative ballet, which establish the aesthetics of consonance, antimimesis and display (instead of experience), as well as the multivariant implementation of the musical and theatrical concept (concert, theater stage, etc.). The works of the American composer D. Cage, the Russian composer V. Martynov, the Belarusian composers V. Kuznetsov, L. Simakovich, A. Korotkina were selected as analytical material.