The suffix "bis" at the end of an opus number often means the piece is an arrangement or adaptation of another work. In this case it was appended by Tchaikovsky's publisher, linking it to the then-recently published Grand Sonata in G Major for piano, Op. 37, although no sound musical relation exists between the two works. Here, Tchaikovsky wrote 12 separate pieces as part of a commission from Nikolai Bernard, publisher of the monthly music magazine, Novelliste. The composer was to provide an appropriate piece for each of the 12 issues of the magazine, a work reflecting feelings or images associated with the month in the title.
January, subtitled "At the Fireside," has an intimate mood, tinged with regret and gentle playfulness, and featuring an attractive Schumann-esque main theme. February ("Carnival") is festive and joyous, the music jaunty and hardly divulging images of snow and dark nights. March ("The Song of the Lark") reverts to a mood similar to that heard in January, but featuring sparser textures and a greater sense of melancholy, as though a feeling hovers that winter will not soon end. April ("Snowdrop") is bright and seems to usher in spring, albeit a spring with a few clouds and rain storms.
The fifth piece here, May ("Starlit nights"), is sweet in its ascending arpeggios, though its theme turns stately on the lower register of the keyboard. The brief middle section is lively but does not break the generally intimate feeling. June ("Barcarolle") has become one of the most popular pieces from the set: its melody is memorable, sounding Chopin-esque in its sweet gloom and mixture of happiness and sadness. July ("The Song of the Reapers") is the briefest of the 12 pieces, but manages several mood swings, moving from the proud to the industrious, then to the playful, maintaining a joyous demeanor throughout.
August ("Harvest") is busy and a bit hectic in the outer sections, but the central portion is simple and lyrical, unhurried and calm. September ("The Hunt") is regal in the fanfare-like music of the first part, but then turns demure for a time while the more garish elements from the opening gradually infiltrate to retake center stage. October ("Autumn Song") is another popular piece, with a life of its own apart from this set. Its slow main theme is melancholy, featuring a refrain-like phrase of mostly ascending notes that is the heart of its sad nature.
November ("Troika") is hardly less popular than June or October. It is bright in mood and direct in its expressive language, and offers a playful, mischievous middle section. December ("Christmas") is almost childlike in its charming waltz, the music seeming to yearn for orchestral dress and placement in one of the composer's ballets. Typical performances of this whole set can range from 35 to 45 minutes.