You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Frédéric_Chopin

Context:
J. Barrie Jones suggests that "amongst the works that Chopin intended for concert use, the four ballades and four scherzos stand supreme", and adds that "the Barcarolle Op. 60 stands apart as an example of Chopin's rich harmonic palette coupled with an Italianate warmth of melody." Temperley opines that these works, which contain "immense variety of mood, thematic material and structural detail", are based on an extended "departure and return" form; "the more the middle section is extended, and the further it departs in key, mood and theme, from the opening idea, the more important and dramatic is the reprise when it at last comes."

Question:
What form does Temperley feel that Chopin's ballades and scherzos are based on?

departure and return