Since he composed many piano pieces, he was called the poet of the piano. Most of Chopin's works are for solo piano, though he also wrote two piano concertos, a few chamber pieces and some songs to Polish lyrics. His piano works are often technically difficult, especially because deep expression is involved along with the importance of considering each detail in his music. Chopin also created the instrumental ballade, along with the addition of new ideas to the piano sonata, mazurka, waltz, nocturne, polonaise, étude, impromptu, scherzo and prélude. All of Chopin's works involve the piano.