I recently saw a Twitter meme of Ken Ham making a crude appeal to a presuppositionalist type of argument against all non-Christians, not just atheists. I don’t want to deal with any potential licensing issues with the image, so rather than display the image on my blog instead I’ll quote the words below.
Non-Christian scientists are really borrowing from the Christian worldview to carry out their observational science. Think about it. When they are doing observational science, using the scientific method, they have to assume the laws of nature, they have to assume the uniformity of nature. If the universe came about by natural processes, where did the laws of logic come from? Did they just pop into existence? Are in a stage now where we only have half logic? How do you account for the laws of logic and the laws of nature from a naturalistic worldview?
There’s an expression, “target-rich environment.” Well, what we have here is a fallacy-rich quotation. In fact, this is so confused it’s hard to know where to begin, although it was tempting to begin by writing, “Actually, no, Mr. Ham, ‘we’ do not have half logic, but maybe you do.” But let’s get serious.
First, I don’t know if Ken Ham is a presuppositionalist or simply using an argument popular among presuppositionalists, but, like them, he is confusing naturalists with non-Christians. At the risk of stating the obvious, a non-Christian doesn’t have to be a naturalist. Even if, for the sake of argument, it were the case that naturalism could not account for the laws of logic and the laws of nature, it wouldn’t follow that other worldviews–worldviews which are incompatible with both naturalism and Christian theism–could not account for the laws of logic or the laws of nature. What we need is an argument which shows why these other non-Christian, non-naturalistic worldviews cannot account for them. His meme does not provide such an argument.
Second, there is something odd about Ham’s first two questions, especially from a Christian perspective. The questions seem to assume that “the laws of logic” are material objects like rocks and trees. Surely Ken Ham doesn’t think of “the laws of logic” that way because he is a Christian theist. So why does he ask his first two questions? The most charitable interpretation of his meme is that he treats “naturalism” and “materialism” — i.e., the belief that matter is all that exists — as synonyms. If one believes that matter is all that exists and one believes that “the laws of logic” exist, then asking “where did the laws of logic come from” is no different than asking “where did galaxies come from?”
I’m not going to fault him for that, since the word “naturalism” is notorious for having so many different definitions. But, speaking as a self-identified naturalist, that’s not how I define the word “naturalism.” Following Purdue University philosopher Paul Draper, I define the word naturalism to mean “the hypothesis that the universe is a closed system, which means that nothing that is not part of the natural world affects it.” So defined, “naturalism” is logically compatible with the existence of abstract objects. So one option for a “naturalist” (in my sense) is to simply adopt some sort of Platonism about “the laws of logic” and, accordingly, deny that the laws of logic ‘came from’ anywhere.
But, just to be extra charitable to Mr. Ham, let’s assume that his intended target is materialism, which is logically incompatible with abstract objects. This leads to the third problem for this type of argument. Raising questions about how naturalism can account for X does not, by itself, show that theism can account for X. It is one thing to wax eloquently about the horrible implications of denying X and to ask how H1 account for X. It is quite another thing to provide an argument for the claim that H1 cannot account for X. Merely asking questions about X on H1 is not an argument for the claim that H1 cannot account for X. And it is yet another thing to provide an argument for the claim that H2 does account for X. Simply asserting that H2 accounts for X is not an argument for the claim that H2 accounts for X. In short, what’s needed is an actual argument, not a series of questions. Like much of the presuppositionalist literature, I do not find such an argument in Ham’s meme.
Fourth, I assume that the laws of nature is Ham’s way of referring to Hume’s problem of induction. If so, then, again following Paul Draper, I think the answer is that, God or no God, induction is justified because uniformity is intrinsically more probable than variety. And notice that this answer does not depend upon induction, so it avoids circularity.
Finally, what about “the laws of logic?” Again, Ham hasn’t spelled out an argument. Instead, I’ll just close with this. If we’re allowed to start outside of what can be justified by reason alone (and instead go with presuppositions), then it’s far from obvious why the belief, “the laws of logic are justified,” is any less worthy of being presupposed than, say, the belief “God exists,” much less the belief, “Christian theism is true.”All of these claims entail that the laws of logic are justified, but the latter two statements entail extra claims about what exists and so on parsimony grounds –and if everything else is held equal — the former is to be preferred over the latter.
 D. Gene Witmer, “Atheism, Reason, and Morality: Responding to Some Popular Christian Apologetics,” talk given to the Atheist, Agnostic, and Freethinker Student Association, University of Florida, September 26, 2006.