As I read it is becoming more clear to me that folks like Van Til, Schaeffer, and Bahnsen did not invent the idea that Modern Philosophy has borrowed turf from Christianity. Van Til was critical of Medieval Philosophy for being too rationalistic but Ettiene Gilson in his The Spirit of Mediaeval Philosophy argues that Modern Philosophy borrowed just as much from Augustine as it did from Plato and Aristotle. He notes that philosophical works from the 17th and 18th centuries would be difficult to explain without taking into account the “Christian Philosophy” of the Medievals, who may have overemphasized man’s reasoning capabilities but never allowed that reason to contradict the fundamentals of faith:
Open for example the works of Rene Descartes, the reformer of philosophy par excellence, of whom Hemelin went so far as to say that “he is in succession with the ancients, almost as if – with the exception of a few naturalists – there had been nothing but a blank between.” What are we to make of this “almost”? Consider, to start with, the title of the Meditations sur la metaphysique, “in which are demonstrated the existence of God and the immortality of the soul.” Consider, again, the close kinship of Descartes’ proofs of God with those of St. Augustine or even those of St. Thomas. It would not be at all difficult to show that his doctrine of liberty owes a great deal to the mediaeval speculations on the relations between grace and free-will – a Christian problem, if ever there was one. (Gilson, p. 13)
Gilson also points out that Hume, in his pronouncement against causality, borrowed heavily from Malebranche. “Now to whom does Malebranche appeal? To St. Augustine quite as much as to Descartes.” (Ibid., p. 15)
BTW: Gilson wrote this in 1931.