The title page bore a dedication to Thérèse von Trattner, who was one of Mozart’s pupils in Vienna. Her husband was an important publisher as well as Mozart’s landlord at the time. Eventually, the Trattners would become godparents to four of Mozart’s children.
The sonata was composed during the approximately 10-year period of Mozart’s life as a freelance artist in Vienna after he removed himself from the patronage of the Archbishop of Salzburg in 1781. It is one of the earliest of only six sonatas composed during the Vienna years, and was probably written either as a teaching tool or for personal use. Sonatas during this time were generally written for the domestic sphere - as opposed to a symphony or concerto, they were designed to convey ideas in a small, intimate setting.
A typical performance takes about 18 minutes.
The work has three movements:
The first movement is written in sonata form. It begins with a fiery Mannheim rocket figure, which appears twice in the first subject, or theme, which makes up m.1 - m. 19. The second subject, which is written in E-flat major, the relative major of C-minor, first appears in m.23- m.71.The exposition begins transitioning at m. 71 to the development, which spans m.75 to m. 99. This portion of the sonata is the most unstable harmonically, running through both F minor and G minor before returning to C-minor. The recapitulation occurs from m.100 to m. 168, and the coda ends the piece from m. 168 to m. 185.
The slow movement is written in rondo form and in E-flat major. It is graceful and tranquil and provides a strong contrast with the first and third movements. The principal theme, or the A subject, occurs from m.1 - m.7. The overall form of the movement is ABACA, with a coda at the end from m. 47 to m. 57.
The third movement returns to the dramatic quality of the first movement. It is written in sonata-rondo form. The first subject in the tonic is quite long, and first appears from m.1 to m. 44, then links to the second subject in E-flat major, which appears from m. 47 to m.96. The principal subject returns in incomplete form from m.103 to m.145, and also provides a link to the next section. In sonata form, it would be called the development. However, it is fairly short, only running from m. 146 to m. 166, and could be simply termed an episode. The episode leads to the recapitulation, which begins with a modified second subject in E-flat major. Subsequently, the principal subject returns in the tonic, and portions of the episode return from m. 275 to m. 287 before the coda at the end from m.288 to m.319. The piece finishes with two dramatic chords.
The Fantasy in C minor, K. 475, was completed some seven months after the C minor sonata. Mozart recorded the date of completion as May 20, 1785 in his private catalogue of works. Opinions have differed whether Mozart intended the two to be performed together. Although they were published together as the same opus, Mozart sometimes performed the pieces separately.
The Fantasy has by nature a more improvisational quality than the subsequent sonata, and the pairing presents a classical correlation to the baroque combination of fantasy and fugue. Both the fantasy and sonata are linked by a focus on the bass register and octaves in the bass clef. The styles of both Muzio Clementi and C. P. E. Bach have been suggested to have influenced the composition of the fantasy, whether consciously or subconsciously.
It is said that Mozart wrote the Fantasy as a reconstruction of the improvisation he made before writing the sonata.
The Piano Sonata No. 14 in C minor is only one of two sonatas Mozart wrote in the minor key, the other being the great Piano Sonata No. 8 in A minor, K. 310, which was written six years earlier, around the time of the death of Mozart's mother. Mozart was extremely deliberate in choosing tonalities for his compositions; therefore, his choice of C minor for this sonata implies that this piece was perhaps very personal work. The key of C minor is generally associated with tragic, violent emotions and the battle with fate. Other significant compositions in C minor (which have strikingly similar main themes) are Beethoven's 3rd Piano Concerto, opus 37 and Mozart's own Piano Concerto No. 24, K. 491.
An original autograph of the two pieces was rediscovered in 1990 at the Eastern Baptist Theological Seminary in Philadelphia by Judith DiBona, an amateur pianist and Accounting Manager at Eastern’s sister school. Eugene K. Wolf at the University of Pennsylvania was contacted to identify and authenticate the manuscripts. He emerged with findings concerning the time of composition between the movements of the sonata and the fantasy, which were published in The Journal of Musicology in 1992. First, his findings further confirmed that the Fantasy and Sonata were written independently due to differences of stave spans, paper-types, and even ink color in between the two manuscripts. Wolf also found differences in paper types between the first and third movements of the sonata and the second Adagio movement, which implies that the second movement was written down at a separate time from the rest of the sonata. He theorizes that the second movement was composed the earliest as an instructional piece for Thérèse von Trattner. Since the second movement is in rondo form and slower than the others, it could exist independently from the sonata more easily than the other movements.
“Without question this is the most important of all Mozart’s pianoforte sonatas. Surpassing all the others by reason of the fire and passion which, to its last note, breathe through it, it foreshadows the pianoforte sonata, as it was destined to become in the hands of Beethoven.” (translated from Köchel’s Catalogue)
Indeed, Mozart's sonata feels in several ways prophetic of the Pathétique (which it predates by roughly fifteen years), and both works share a similar overall plan. The spacious second movement makes use of a theme remarkably similar to that of the second movement, "Adagio cantabile," of Beethoven's own great C minor sonata, the Piano Sonata No. 8 in C minor, "Pathétique".