Schubert wrote a great deal of music for solo piano including his sonatas, sets of Landler dances, the Moments Musicaux and his eight Impromptus. The two sets of impromptus for pianoforte are amongst the greatest of these collections and to this day are much loved by pianists the world over. These pieces can be played either individually or as part of their individual sets; indeed, recordings of the Impromptus often contain both sets.
As mentioned above there are two sets of four impromptus, Opus 90 D. 899, and Opus 142 D 935. Both were composed in 1827 and published during Schubert's lifetime. Opus 90 No. 3 in G Flat is particularly known for its inclusion in the Australian film The Getting of Wisdom, directed by Bruce Beresford and produced in 1978. The pianist Alfred Brendel also occasionally introduced this piece as an encore during his concerts.
The first set of impromptus, Opus 90, contains impromptus in C minor, E flat, G flat and A flat major. In all of the impromptus it is difficult to specify the exact modality in which the work is tuned, whether major or minor, because Schubert fluctuates so much between modalities. Indeed, he will begin a piece in the minor and then finish in a triumphant major. Some very unusual modulations occur; the A flat impromptu starts very definitely with a series of A flat major arpeggios, and then suddenly drops into the key of C sharp minor for its middle section! The tonic of C sharp minor of course is also the tonic of D flat minor - the dominant of A flat. Using the C sharp minor however allows Schubert to develop harmonies in a different way from that which he would have done had this section been in D flat minor (also incidentally making the music easier to read, write the notation and to play).
The second set of impromptus, Opus 142, is even more individualistic. The opening drama of the F minor impromptu develops into a complex melody played by the left hand, crossing back and forward over the right hand which plays the arpeggio accompaniment. No 2 of this set in A flat major, consists of a minuet and trio with the gentle melodic opening, almost choral in style, interspersed with the middle section of triplets, the bottom note of each forming the melody.
Opus 142 No. 3 is a theme and variations and it is at this point that the music becomes really virtuosic. None of the impromptus are easy but can be played by any well trained pianist of around Associated Board Grade 8; the later variations in this piece become more and more complex. The whole set of eight pieces (two groups of four) is completed by the final, dramatically virtuosic F minor Opus 142 No. 4; its glittering runs and triumphant development make it a fitting work to finish the two collections of inpromptus.
These works for piano are amongst the greatest of Schubert's piano music and are well worth getting to know. Pianists wishing to learn to play them should obtain, if possible, a good Urtext edition of the music as Schubert's notation is very clear; you will never in any case play the pieces the same way twice. as at this level there is always room for interpretational development during playing.
For those wishing to get to know the impromptus, Schubert: The Complete Impromptus, a recording by the great pianist Alfred Brendel, cannot be recommended too highly.