Recent (that is, pre-1992 A.D.) Reformed theology can be sadly described as a generation arising “which knew not Turretin.” To paraphrase Galadriel in The Fellowship of the Ring: Some things that should not have been forgotten were lost. Turretin’s categorical form of argumentation was one of those “things.” Turretin’s strength is in identifying precisely the issue in question. This allows him to accept and acknowledge points of agreement with his opponents,rather than simply seeing everything as “Arminian.” Recent Reformed (and Arminian-Papist) polemics have all focused on a few issues: predestination, free will, assurance, the Canon, etc.
Turretin understood that there were other issues, too: anthropology, middle knowledge, etc. which also need to be addressed. The English translation of Turretin fills a woeful lacuna.
While it might be anachronistic to label Turretin’s epistemology as “Common Sense Realism,” one can see similarities. Reason is not ultimate, but it is a reliable guide not only in matters of “nature” but also in “grace.” In using reason in theology, Turretin distinguishes between two extremes. Unlike the irrationalists (Anabaptists, Lutherans, Eastern Orthodox), reason can function as a principia in theology. It is not the fundamental principia upon which all theology rests (that is the principium essendi); rather, it is an instrumental principle (I: 24).
Turretin does ascribe a functional role to “natural reason.” Natural man, whatever that phrase means, can understand axiomatic truths (29-30). Reason is of particular instrumental use in terms of inference and middle premises. For example, Christ’s ubiquity denied in the following way: “Besides, while the theologian uses arguments drawn from reason, he does it rather as a philosopher rather than as a theologian. As to the ubiquity of the body of Christ, we reject this doctrine both philosophically and theologically, because it is absurd and contradicts the first principles of theology and philosophy.” In other words, the definition of a human nature is that it isn’t ubiquitously extended into space. The Lutheran (and EO) view of the communicatio extends it ubiquitously in space. Therefore, such view is wrong.
Turretin explains:[T]he middle term [in the theological syllogism] is not taken from reason, but scripture…For example, I deny that the glorified body of Christ is everywhere, having taken from Scripture this mean, that it is a real body” (26-27)
Canon and Scripture
So did the Church create the canon? If so, doesn’t that mean the church has authority over the canon? Turretin meets this challenge head-on and notes, given what everyone accepts about principia, proves that the Protestant position is the only feasible one. If the Scriptures come primarily from God—as all must concede—then they bear God’s authority. If they bear God’s authority, then they get their primary authentication from God (85ff). That the church was instrumental in delivering aspects of a canon (I still dispute that the church gave a neat canon) no one denies. That is precisely the point: the church was instrumental, not original. Only the Protestant doctrine of magisterial and ministerial authority can make sense of this point.