The Fifth Book against Eunomius is on the Holy Spirit, and therefore, even if it were of indubitable genuineness, it would be of comparatively little importance, as the subject is fully discussed in the treatise of his mature life.  A reason advanced against its genuineness has been the use concerning the Holy Ghost of the term God.  (§ 3.)  But it has been replied that the reserve which St. Basil practiced after his elevation to the episcopate was but for a special and temporary purpose.  He calls the Spirit God in Ep. VIII. §11.  At the time of the publication of the Books against Eunomius there would be no such reason for any “economy” cf. remarks in § vi. p. xxiii. of Prolegomena. as in 374.