A consistently Christian method of apologetic argument, in agreement with its own basic conception of the starting point, must be by presupposition. To argue by presupposition is to indicate what are the epistemological and metaphysical principles that underlie and control one’s method. The Reformed apologist will frankly admit that his own methodology presupposes the truth of Christian theism. Basic to all the doctrines of Christian theism is that of the self-contained God, or, if we wish, that of the ontological trinity. It is this notion of the ontological trinity that ultimately controls a truly Christian methodology. Based upon this notion of the ontological trinity and consistent with it, is the concept of the counsel of God according to which all things in the created world are regulated.
– Cornelius Van Til, The Defense of the Faith p. 121