The structure of a fugue is the result of process rather than the result of using a conventional template. Bach's early fugues resemble those of Buxtehude, canzoni and ricercars. Links are not used consistently throughout a fugue, a feature which helps one to determine the contents of the subject. Connecting passages in which the subject is not stated intact, connects one statement of the subject to the next. An episode is any passage that does not include the whole subject.
Episodes use motives and fragments from first part of fugue, often in sequences.
In the middle section of the fugue, entries and episodes may alternate, a pairing of subject matter and motive development passages. The middle section of a fugue may contain no episodes and proceed from middle entry to middle entry sans linking episodic passages. Usually based on motives and fragments stated in first part of fugue. Various key plans created through subject entries. Integral to structure of fugue.