Presuppositonalists insist that the senses are not a reliable way to discover truth, and yet they trust them implicitly when it comes to dinnertime: they do not fear that the cheeseburger is actually a rattlesnake poised to strike. Furthermore they have to use their eyes or ears or hands in order to hear or read the Bible, and yet they are perfectly willing to trust their senses for this duty.
Presuppositionalists insist that man’s intellect cannot be trusted because of the effects of the Fall, and yet they must exercise their own intellects when performing exegesis of the Bible. And they are perfectly willing to trust their intellects when doing so.
Presuppositionalists may attempt to escape these dissonances by claiming that the Holy Spirit guides them, but they do not all agree among themselves about the truth. Furthermore this is really special pleading, because those who disagree with them concerning the reliability of the senses and of reason may make the same claim to have been guided by the Spirit.