All truth is God's truth

In A Statement of Evangelicals and Catholics Together: "That They May Have Life" there is found this about the ability of reason to discern truth. Perhaps more importantly there is the affirmation that God is the source of all truth, whether we receive it from His revelation or find it by the study of His creation.

"Between Evangelicals and Catholics there have been long-standing differences on the capacities of human reason. To put it too briefly, Evangelicals (and the Protestant traditions more generally) have accented that human reason has been deeply corrupted by sin. Catholics, on the other hand, while recognizing that human reason has been severely wounded by sin and is in need of healing, have held a higher estimate of reason’s capacity to discern truth, including moral truth. We, as Evangelicals and Catholics together, affirm that the knowledge of God necessary for eternal salvation cannot be attained by human reason alone apart from Divine revelation and the Holy Spirit’s gift of faith’s response to Jesus Christ the only Savior....

We also affirm together that human reason, despite the consequences of sin, has the capacity for discerning, deliberating, and deciding the questions pertinent to the civil order. Some Evangelicals attribute this capacity of reason to “common grace,” as distinct from “saving grace.” Catholics typically speak of the “natural law,” meaning moral law that is knowable in principle by all human beings, even if it is denied by many (Romans 1 and 2).... Both faith and reason are the gift of the one God. Since all truth has its source in Him, all truth is ultimately one, although our human perception of the fullness of truth is partial and inadequate (1 Corinthians 13:12). Thus do we invite those who disagree, including those who do not share the gift of faith in Christ, to join with us in attempting to move beyond “culture wars” to a reasonable deliberation of the right ordering of our life together." [emphasis added]