A thought I just had as I am studying Van Til's "The Defense of the Faith".
There is an inverse proportion between what is most knowable in itself, and what is easiest for man, by nature, to know. One of the essential differences between classical apologetics and presuppositional apologetics is that classical apologetics begins with what is easiest for man, by nature, to know, and seeks to bring man to that which can be known by man of that which is most knowable in itself; presuppositional apologetics begins by claiming that one must presuppose that that which is most knowable in itself is true in order to truly know that which is easiest for man, by nature, to know, and then seeks to show man that even those things which are easiest for him to know only get their truest "meaning" when understood in light of that which is most knowable in itself.
Though there may be some major difficulties with one (or both) of these approaches, it is important to note that they neither contradict, nor exclude, each other. Both approaches (in at least this one element) can and should be used in any well rounded apologetics.