Bach - Prelude no.18... Isn't this a fugue ?

[kghayesh]

Check Prelude no.18 in G# minor from book 1. Isn't this a fugue. Watch the theme repeated so many times all over the piece. It is full of counterpoint also.

I just want to know how this is not a fugue ?

[phil13]

Because the definiton of a fugue is that it has a distinct, fugal exposition, in which all of the voices play the subject and its answer one after another (the subject has to be stated by itself the first time it is played).

Prelude No.7 in Eb from Book I is a fugue- in fact, it is a double fugue since it has two subjects. But Prelude No.18 is not. The theme could be all that is played through an entire work. That makes it concentrated, not fugal. 

Phil

[kghayesh]

Thanks. Now I understood why it is not a fugue !!