''Pensieri notturni'' (''night thoughts'') was created in 1961 during the peak of the composers period of sonorist writing. They are designed for chamber orchestra, hence the utmost importance of every detail, every sound, or sequence of a single instrument. The essence of this piece is the flickering sound image, textural flexibility, instability and volatility of tone, transience of motifs scattered in different registers.
They were first performed on April 21, 1961 at the Venice Biennale by the Kraków Philharmonic Chamber Orchestra conducted by Andrzej Markowski, and then by the same artists, 23 September 1961 at the Warsaw Autumn Festival. The composer herself said about the piece, It might apparently seem (...) that this is somehow programme music. But only apparently. (...) The distinctive feature of the work - after all, what happens in it is an obsessive adherence to certain sounds expanding and narrowing again.This composition was to be an attempt to pass on something that maybe the composer takes from somewhere. The content of the work forced me to treat the instruments in a special way, especially the strings (...).
The sound material that I use in the composition is not based on any existing system; it has been strictly arranged by myself. The only borrowed element is the principle of non-recurring notes. The work is characterized by an obsessive use of certain notes expanding and returning to their previous states. The composition is meant to be an attempt at conveying something received by the composer perhaps from somewhere. The contents of the composition have made me treat the instruments in a special way, the strings in particular. [G. Bacewicz, an excerpt of personal notes, Ruch Muzyczny 1994, No. 1]