For good reason, one might find John Calvin referred to as an “anti-speculative” theologian. But as with so many other monikers applied to Protestant theologians (e.g. “anti-scholastic”), one must take the label in its relative rather than its absolute signification. When confronted with biblicism, Calvin could sound a philosophical and “speculative” note.
B.A. Gerrish observes this tendency: in response to the biblicism of Giorgio Biandrata 1, Calvin concludes, in Gerrish’s gloss, that “within carefully defined limits we may, after all, philosophize in moderation, not speculating further than Scripture raises us but only giving its simple and genuine meaning.” This leads Calvin to an endorsement of the validity of non-Scriptural terminology in discussing the Godhead, such as “consubstantial” and “Trinity of Persons.”
Gerrish points to two passages for his summation. The first is Institutes 1.13.21, which serves as a sort of preface to Calvin’s refutation of various Trinitarian heresies. (He has already applied such terminology to the refutation of heresies earlier in 1.13 as well.)
The second is from a work against Biandrata, the Ad Blandratae quaestiones responsum (“An Answer on the Matters Biandrata Has Called into Question”). Recall, again, that “speculation” is a relative matter: for an anti-Trinitarian like Biandrata, it is Calvin who wears the black hat of the speculative theologian. It is a hat he wears for this purpose, but modestly: if you got it, don’t flaunt it.
But those who hatefully slander the orthodox faith on the pretext that speculation (speculatio) about the one essence and three Persons is useless betray their base malice, because we do not speculate (speculamur) further than Scripture takes us, but we render its genuine and simple sense. For no one will acknowledge Christ as his God from the heart unless he has apprehended the diverse Persons in the unity of the essence–for a plurality of gods, which some fictively fashion, is an accursed madness. 2
Notice that Calvin twice self-referentially uses related terms that he himself and his allies frequently deployed against their own opponents in the Church of Rome. A blessed (or cursed?) inconsistency? No, not really. Or, really, not at all. Calvin makes his own position fairly clear: there are instances in which “philosophy” or philosophical reasoning (that is, “speculation”) can serve as a handmaiden to theology, but it must be rigorously restrained to the explication and clarification of what the Word teaches (or, one might add, of what must necessarily be true for what the Word teaches to make sense); it must be limited by the Word. In Calvin’s view, his Roman opponents did not observe the qualification, while his anti-Trinitarian opponents did not acknowledge the ancillary role of “speculation” for understanding the Scripture they claimed to be trying to protect. Calvin himself, on the other hand, wishes to avoid both these ditches through a chastened and strictly demarcated speculative theology.
Three cheers, then, for the speculative Calvin.