 Turnbull is committed to a form of reliabilism according to which the faculties that we have by the frame or constitution of our nature are trustworthy. It is not simply that we are so constructed that we cannot but accept their deliverances; it is that we are also entitled to accept them. Turnbull, a deeply committed Christian, believed that the author of our nature would not have so constituted us as to accept the deliverances of our nature if our nature could not be relied upon to deliver up truth. We are in the hands of providence, and live directed towards the truth for that reason. This doctrine has been termed ‘providential naturalism’, and bears a marked resemblance to the language and also to the substance of the position held by Turnbull’s pupil Thomas Reid.