This splendid fugue—one of the most perfect of the 'Forty-Eight'—is a remarkable example of Bach's power of letting art conceal art. There is not one which flows more naturally and unconstrainedly, and yet there is not one which is fuller of scientific device. This will appear from our analysis.
309. Let us first look at the subject. We see here an exception to the general rule given in § 29, that with a downward leap of a fifth the first note will be dominant, and the second tonic. The subject begins with a leap from tonic to subdominant, and consequently takes a real answer. Had D been a dominant, the key of the fugue would have been G, and the answer
As C sharp is not used in the subject, the key is doubtful at first; in such cases the answer always decides the point.
310. As Bach intends the fugue to contain a large amount of close imitation and stretto, there is no regular countersubject (§ 176); but instead of this, the last half of the subject is ingeniously made to serve as a counterpoint to the first half,