Van Til engages with the view of B. B. Warfield concerning the relation of systematic theology to apologetics and the nature of apologetics itself (Introduction to Systematic Theology, p17-19). Van Til considered Warfield’s distinction between the method of systematic theology and the method of apologetics as mistaken.
For example, Warfield considers apologetics to be prior to systematic theology:
“…apologetics supplies to Christian men the systematically organized basis on which the faith of Christian men must rest.” (Apologetics, Works, Vol.9)
“Apologetical Theology prepares the way for all theology by establishing its necessary presuppositions without which no theology is possible — the existence and essential nature of God, the religious nature of man which enables him to receive a revelation from God, the possibility of a revelation and its actual realization in the Scriptures. It thus places the Scriptures in our hands for investigation and study.” (The Idea of Systematic Theology, Works, Vol.9)
The discipline of systematic theology, therefore, does have presuppositions (the existence of God and the infallible revelation of Himself in Scripture, etc), but its work would be a speculative exercise unless these presuppositions were established by the work of apologetics. But on what basis does apologetics establish their truth? By drawing upon the historical and natural sciences, according to Warfield. According to this method, apologetics is necessarily presuppositionless.
However, Van Til claims:
Warfield often argues as though apologetics must use a method of approach to the natural man that the other disciplines need not and cannot use… All the disciplines [including apologetics] must presuppose God, but, at the same time, presupposition is the best proof. Apologetics takes particular pains to show that such is the case. (Introduction to Systematic Theology, p18-19)
And concludes by stating that:
“…apologetics stands at the outer edge of the circle of systematic truth given us by systematics in order to defend it.”(ibid, p19)
In summary: For Warfield, apologetics establishes the truth of the presuppositions of systematic theology. For Van Til, apologetics defends the truth of those presuppositions.