Letters, seemingly love letters, penned by Beethoven but ultimately left unsent, were preserved for posterity with an unknown addressee, sparking scholarly debate over the identity of the recipient, the so-called "Immortal Beloved." One of the candidates was Countess Therese von Brunswick. A daughter from a Hungarian noble family, she received piano lessons from Beethoven along with her sister, Josephine. (Incidentally, Therese was later excluded from the "Immortal Beloved" candidates, with Josephine remaining a strong contender; however, Antonie Brentano, another prominent candidate, is now widely considered to be the person in question).

Therese was indeed a woman of high musical talent, to the extent that she performed a piano concerto by Antonio Rosetti publicly at the age of six. Later, in 1828, Therese, a woman of great talent, established the first kindergarten in Hungary. Beethoven's Piano Sonata Op. 78 was composed in 1809 and dedicated to Therese in 1810, which is why her name has become the common title for the work.

Positioned between the "Waldstein" and "Appassionata" sonatas, which are prime examples of his middle period's dramatic style, and the "Les Adieux" sonata, which often draws biographical attention, Op. 78 is a smaller work, structured in two movements. However, this does not mean it should be valued less than the surrounding works. During his middle period, alongside large-scale compositions, Beethoven also wrote pieces that, despite their concise length, demonstrated ingenious compositional techniques, such as the String Quartet "Serioso" Op. 95. Op. 78 should rather be understood as belonging to this category. Given that it is the only one of Beethoven's piano works to be written in F-sharp major, a key with six sharps, it is clear that simplicity was not a primary consideration from the outset. As noted in the commentary for each movement, Op. 78 is a work that aims to stimulate the listener's thought processes rather than present a clear structure. By comparing the two movements, one can discern that these two movements, which might initially sound as if they flow freely, are connected in various ways.