Joel claims that presuppositionalists make God second to epistemology. That statement is fallacious. In fact, it is nonsensical.

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Epistemology is the study of the source and nature of knowledge. Presuppositionalists say that God is the source of all knowledge. That means God answers the epistemelogical question.
This is nothing new. It may be a relatively new way of stating things, but it is not a new view.
Calvin said,
in the first place, no man can survey himself without forthwith turning his thoughts towards the God in whom he lives and moves; because it is perfectly obvious, that the endowments which we possess cannot possibly be from ourselves; nay, that our very being is nothing else than subsistence in God alone. In the second place, those blessings which unceasingly distil to us from heaven, are like streams conducting us to the fountain. Here, again, the infinitude of good which resides in God becomes more apparent from our poverty
John Calvin, Institutes of the Christian Religion (Bellingham, WA: Logos Research Systems, Inc., 1997).
not a particle of light, or wisdom, or justice, or power, or rectitude, or genuine truth, will anywhere be found, which does not flow from him, and of which he is not the cause; in this way we must learn to expect and ask all things from him, and thankfully ascribe to him whatever we receive. For this sense of the divine perfections is the proper master to teach us piety, out of which religion springs. By piety I mean that union of reverence and love to God which the knowledge of his benefits inspires. For, until men feel that they owe everything to God, that they are cherished by his paternal care, and that he is the author of all their blessings, so that nought is to be looked for away from him, they will never submit to him in voluntary obedience; nay, unless they place their entire happiness in him, they will never yield up their whole selves to him in truth and sincerity.
John Calvin, Institutes of the Christian Religion (Bellingham, WA: Logos Research Systems, Inc., 1997).
Calvin understood that God is the source of all knowledge. He did not understand that except for the fact that he found that truth in Scripture. He also saw that man must subject his knowledge and his passions to God as the supreme authority.
Scripture teaches us that man knows God by nature, knows that God is the absolute and supreme authority, and that man suppresses that knowledge (See Romans 1:18-21).
Calvin stated,
how can the idea of God enter your mind without instantly giving rise to the thought, that since you are his workmanship, you are bound, by the very law of creation, to submit to his authority?—that your life is due to him?—that whatever you do ought to have reference to him? If so, it undoubtedly follows that your life is sadly corrupted, if it is not framed in obedience to him, since his will ought to be the law of our lives. On the other hand, your idea of his nature is not clear unless you acknowledge him to be the origin and fountain of all goodness. Hence would arise both confidence in him, and a desire of cleaving to him, did not the depravity of the human mind lead it away from the proper course of investigation.
For, first of all, the pious mind does not devise for itself any kind of God, but looks alone to the one true God; nor does it feign for him any character it pleases, but is contented to have him in the character in which he manifests himself always guarding, with the utmost diligences against transgressing his will, and wandering, with daring presumptions from the right path. He by whom God is thus known perceiving how he governs all things, confides in him as his guardian and protector, and casts himself entirely upon his faithfulness,—perceiving him to be the source of every blessing, if he is in any strait or feels any want, he instantly recurs to his protection and trusts to his aid,—persuaded that he is good and merciful, he reclines upon him with sure confidence, and doubts not that, in the divine clemency, a remedy will be provided for his every time of need,—acknowledging him as his Father and his Lords he considers himself bound to have respect to his authority in all things, to reverence his majesty aim at the advancement of his glory, and obey his commands,—regarding him as a just judge, armed with severity to punish crimes, he keeps the Judgment-seat always in his view. Standing in awe of it, he curbs himself, and fears to provoke his anger. Nevertheless, he is not so terrified by an apprehension of Judgment as to wish he could withdraw himself, even if the means of escape lay before him; nay, he embraces him not less as the avenger of wickedness than as the rewarder of the righteous; because he perceives that it equally appertains to his glory to store up punishment for the one, and eternal life for the other. Besides, it is not the mere fear of punishment that restrains him from sin. Loving and revering God as his father, honouring and obeying him as his master, although there were no hell, he would revolt at the very idea of offending him.
Such is pure and genuine religion, namely, confidence in God coupled with serious fear—fear, which both includes in it willing reverence, and brings along with it such legitimate worship as is prescribed by the law. And it ought to be more carefully considered that all men promiscuously do homage to God, but very few truly reverence him. On all hands there is abundance of ostentatious ceremonies, but sincerity of heart is rare.
John Calvin, Institutes of the Christian Religion (Bellingham, WA: Logos Research Systems, Inc., 1997).
In other words, Calvin saw that man recognizes within himself that God is the source of all knowledge, morality, goodness, and of every gift that he receives. Man is thus morally obligated to honor God by submitting to Him in the manner in which He has revealed to us that we should submit ourselves.
The important thing to see here is not simply the fact that Calvin’s view of man, God, Scripture, and obedience are essentially the same as those of the presuppositionalist, but that Calvin understood that God is the source of all knowledge.
Calvin knew that epistemology was not second to God. God, rather, is the source of all knowledge and the answer to the question epistemology asks. Calvin will continue on to teach (As does the presuppositionalist) that we gain knowledge of God from His Word, the Scriptures. To say that presuppositionalists believe or do otherwise is either to misunderstand that issue before us, or it is intellectually dishonest.
Finally, Joel states ,
When we feel we must infer something upon Scripture, then we are denying the authority of Scripture.
This is definitely an issue of dishonesty. Joel has stated that he does not believe in the authority of Scripture, but he now claims that presuppositionalists are denying the authority of Scripture. One cannot eat his cake and have it, too.
Furthermore, the statement of Joel’s is simply nonsense. It is meaningless, because to infer is to arrive at something through reasoning. You do not infer something UPON Scripture: you infer FROM Scripture. And that is what presuppositionalists do.
If you wish to get some background to this discussion, it starts here, then you can continue here.
Update: I’ve also commented on Joel’s post here and here.