The maturity and originality of concepts found in this Sonata really give birth to a new moment in the piano literature: Schubert puts himself here on a level of universality that transcends gender.
The Sonata Op. 143 should be placed chronologically between the works Alfonso and Estrella and Fierebras. It is not clear why Schubert composed a Sonata for piano when he was in the middle of two Operas: not because he had been asked by a publisher and not because he had been asked by an amateur.
The hypothesis is that the Sonata op. 143 constitutes a moment of dramaturgical research, a study cartoon for theatrical situations.
The character of the piano writing of the first movement, which is totally devoid of coloratura, clearly refers to the orchestra. But even more impressive is the fragmentation of the themes in the cells and the obsessive use of the repetition of the cell. The classic logic of thematic development is thus completely overcome and the thematic progression moves towards tensions that it is not exaggerated to be defined as expressionistic.
The principle of dramatic contrast transferred within the themes, instead of between the different themes, also permeates the second movement. The first theme, which is a very simple harmonized choral, is continually interrupted by a contrasting thematic cell. And, to give more importance and meaning to this cell, Schubert prescribes the use of a pedal, the "sordino", which is no longer mounted on modern pianos and which partially suffocated the vibration of the strings. Both the use of this typically timbral pedal, and a carefully studied piano instrumentation and in some cases (exposition of the first theme) of disconcerting genius, open a conception of sound in space - in orchestra, on the scene, behind the scenes - which turns the keyboard into a theatrical place, a laboratory where situations are simulated in a very different way from the traditional chamber music writing.
In the last movement Schubert instead returns to a more traditional logic of composing with two well-differentiated and contrasting themes (the second is one of those "celestial" melodies for which Schubert is famous) and a clear division of the material within the scheme of the so-called rondò-sonata. The unity of the Sonata, however, is not at all compromised because Schubert gives birth to the first theme from the contrast cell of the first theme of the second movement. The final arises as a commentary on the first two movements and the Sonata becomes the hinge that will let Schubert find in the piano the transfer of his aspirations as a playwright.
