José Rodríguez Alvira
The subject used in Contrapunctus V is a variation by inversion of the subject in which the Art of the Fugue is based. The following image compares both subjects. The notes between parentheses are added notes. There is also a small rhythmic variation in the third measure:
In this fugue Bach will use two counterpoint techniques: the stretto and the inversion. The subject will be used in the original (it is already the inversion of the original Art of the Fugue subject) and inverted form (an equal number of the times). We find both techniques in the exposition: alto and tenor use the subject in the original form, the bass and soprano use the inverted form and each voice enters in stretto.