When there is no entrance of the subject and answer material, the composer can develop the subject by altering the subject. This is called an "episode", often by "inversion", although the term is sometimes used synonymously with middle entry and may also describe the exposition of completely new subjects, as in a double fugue for example (see below). In any of the entries within a fugue, the subject may be altered, by inversion, retrograde (a less common form where the entire subject is heard back-to-front) and diminution (the reduction of the subject's rhythmic values by a certain factor), augmentation (the increase of the subject's rhythmic values by a certain factor) or any combination of them.