One of the most central components of Van Til's presuppositional apologetics method is his transcendental argument. His aim here is to demonstrate that the unbeliever uses 'borrowed capital' from the Christian worldview in order to navigate and make sense of the world but that this borrowed capital does not fit consistently within his worldview. The use of formal logic as well as appeal to morality are two of the most common examples. For example, an atheist cannot appeal to morality in his condemnation of anything, religious or not, because atheism commits one to an emotivist theory of ethics according to which words like "bad", "unjust", "evil" are simply expressions of emotions but have no objective referent. Van Til's point is to demonstrate that the Christian worldview, unlike his opponent's, is able to account for such concepts.
But is this really a consistently 'presuppositional' approach? Keep in mind that Van Til continually emphasizes the importance of presupposing the Christian worldview in his apologetics rather than attempting to find some sort of neutral ground that could function as a kind of court of appeal to which both unbeliever and believer could submit their evidence and obtain an objective result. He denies that this is either possible or compatible with epistemological virtue from a Christian perspective.
One runs into a potential conflict when one tries to square this position with his transcendental argument. According to Van Til, all epistemological claims presuppose an ontological claim and all ontological claim presuppose an implicit epistemological claim. It's on these grounds that he believes that all reasoning is inherently circular and one can never step otuside of one's own worldview to consult a supposedly neutral court of appeal. Given that this is the case, it is difficult to see how one can argue that one's opponent's claims are necessarily internally inconsistent. For example, Van Tillians often make the claim that the atheist is being inconsistent when he or she presupposes the laws of logic in his or her argument, on the grounds that formal logic is only consistent within a worldview which allows for eternal, immaterial or abstract objects, which a materialistic worldview does not allow. But such a criticism already presupposes Christian standards of consistency. These standards of consistency do not necessarily apply to an atheist.
More interestingly for the philosopher of religion is the so-called Wittgensteinian fideism, according to which language does not refer to objective reality; rather, utterances are to be understood only in terms of its use and coherence within a certain worldview. Each worldview itself presupposes its own standards of consistency, rationality and intelligibility and so external standards which critique it, only critique it because they operate according to their own standards of rationality, consistency and intelligibility which are themselves foreign to the worldview being critiqued. Thus, for example, if the Christian argues that the monadic god of the Muslims is evil and monstrous, the Muslim will (indeed, must) define what it means to be "evil" in terms consistent with its understanding of the religious ultimacy from which the concept of evil itself proceeds, and in terms of which it must be defined. Its consistency is therefore upheld and inoculated from any external critiques, Christian or otherwise.