This is my overview of a recent collision between Matt Slick and Alex Malpass, concerning a popular argument for the existence of God. If you know the answer to the question posed in the title of each section, feel free to skip the section.   —SC


What is Presuppositionalism?

“Presuppositionalism” is a brand of Christian apologetics—that is to say, it is a way of defending the truth of Christianity—which maintains that the Christian worldview is the only possible way to account for the existence of rational thought.

It is called “Presuppositionalism” because it espouses that to use logic or engage in rational thought is to presuppose that Christianity is true, even if we don’t realize we are doing so. If Christianity is false, the presuppositionalist asserts, then rational thought could not be possible in the first place. Different presuppositionalists unpack this claim in different ways, but one way is to say that logic itself would not be possible without God existing, since logic and its laws (e.g., the Law of Noncontradiction, which says that “X” and “not-X” cannot both be true simultaneously) are in fact a reflection of God’s ordered mind. Thus, without God, there could be no logical order to the universe, and thus there could be no rational thought.

Presuppositionalists maintain that any use of logic or reason to dispute the existence of the Christian God is necessarily self-defeating: merely by employing logic or rational thought, the non-Christian has lost the debate, since she has unwittingly already assumed the truth of Christianity—a lose/lose.

But what reasons do presuppositionalists give for thinking that the proposition,

“If Christianity were false, rational thought would not be possible in the first place”

…is actually true?

In conversation, the presuppositionalist will typically deny (explicitly or implicitly) that they need to give reasons or arguments for thinking the above proposition is true. Rather, it is presupposed to be true, and the presuppositionalist sees nothing wrong with this. “If you deny that the Christian God is the only way to account for logic and rationality,” he will say, “then let’s see you account for it without God. Give me your best shot; you can’t do it.”

This is called shifting the burden of proof, and it is a subtle but nearly indispensable tool of presuppositional apologetics. It also happens to be a fallacy: “It’s not my job to demonstrate that my assumptions are true;, it’s your job to demonstrate that they are false.”  

For more on presuppositionalist burden-shifting, read this.

Who is Matt Slick?

Matt Slick is the founder and president of CARM (Christian Apologetics and Research Ministries), a Calvinist, minister, and presuppositional apologist. Read this.

What is TAG?

TAG stands for “Transcendental Argument for God,” and is in this case (though not always) a formal presuppositionalist argument for God’s existence, popularized by Matt Slick. Read this.

Who is Alex Malpass?

Alex Malpass is an atheist and critic of presuppositionalism, with a PhD in philosophy from the University of Bristol, specializing in logic and metaphysics.

…He is also the guy who conclusively refuted Matt Slick’s TAG.

Really? What is Alex Malpass’ refutation of TAG?

Read this.

Is Matt Slick aware of Alex’s refutation?

Yes. Matt has read Alex’s blog post above, but struggled to understand it, despite its simplicity. Alex then spent more than two hours trying to explain his refutation of TAG to Matt in a Google Hangout hosted by the YouTube personality, “Bible Thumping Wingnut”. Watch it below.

Has Matt Slick stopped using TAG?

No. Matt Slick now claims that Alex has not refuted TAG, and worse, that Alex never even purported to refute TAG, only to correct Matt’s phrasing of the argument. Watch this:

Is that true, though?

No. Either Matt was not paying enough attention, or he is being dishonest. Read this.

So what is Matt missing?

Basically everything. Matt’s TAG takes the form of a disjunctive syllogism. It always has. Any argument for the existence of God which does not take the form of a disjunctive syllogism (even if it still deals with accounting for logic) is not Matt’s argument but a different argument altogether. 

Matt wants to think that Alex has merely nitpicked the phrasing of the argument, but that the argument will be successful once it’s been reworded properly. This is false.

What Alex’s refutation has demonstrated is that there is no successful way to use a disjunctive syllogism here, no matter how it is phrased, because the argument will always—always—reduce to either a false dichotomy or question-begging, both of which are argumentative failures. This is logically provable. For anyone who understands logic, there is no debate to be had about it.

Okay, walk me through this. What the heck is a disjunctive syllogism?

Logical arguments can take different syllogistic forms. Modus ponens, for example, is when an argument that takes the following form:

1. If p then q.
2. p.
C. Therefore, q.

A disjunctive syllogism (the form Matt’s argument takes) is the kind of logical argument that says, “If we have only two possibilities, and we know that one of those two possibilities is false, then we know that the other possibility is in fact true.”

1. Either p or q.
2. Not p
3. Therefore, q.

In english:

1. Scott is either wearing a red shirt or a blue shirt.
2. Scott is not wearing a blue shirt.
3. Therefore, Scott is wearing a red shirt.

But logic doesn’t concern itself with whether the premises in the above argument are actually true. What if (1) is false because Scott is wearing a green shirt? Or no shirt at all? Logic has nothing to say about that; it only cares about making the right inferences: if (1) and (2) are both true, then (3) has to be true as well.

The argument above is “valid”—(3) inescapably follows from (1) and (2)—but that doesn’t tell us whether it’s “sound”, that is, (1) and (2) are actually true premises. Valid arguments don’t necessarily have true conclusions, but sound arguments do.

How has TAG been refuted, then?

Whenever Matt tries to describe his argument in casual language, he subtly switches back and forth between a version of his first premise that’s true (because it’s a real dichotomy; there is no other logically possible option), and a version that’s false (because it’s a false dichotomy; there are other logically possible options).

The true version is:

1a. Either it’s the case that God exists, or it’s not the case that God exists.

The false version is:

1b. Either God’s existence accounts for the laws of logic, or God’s nonexistence accounts for the laws of logic.

For an interlocutor unfamiliar with this sleight of hand, the dialogue usually goes something like this:

SLICK: “Either God, or no-God. There’s no other possibility, right?”
ATHEIST: “Sure, I can’t disagree with that.”
SLICK: “Good, so either God accounts for the laws of logic, or no-God does.”
ATHEIST: “Umm, sure? I guess?”

Alex Malpass articulates the problem thusly:

“Slick dangles the true dichotomy of ‘God or not-God’ in order to gain assent (as nobody can deny a tautology), but then switches focus to the false dichotomy above without conceding that he now needs to justify the new premise. This is the heart of the Matt Slick Fallacy; it is a bait and switch from a true dichotomy to a false one.”

Still, this bait and switch is not the reason TAG fails, per se. TAG fails because both versions of his first premise (true and false) lead to problems which are fatal. 

Time out: why is (1b) a false dichotomy?

Alex illustrates this with a reduction to absurdity:

1) Either toast, or not-toast.

2) The absence of toast cannot account for the laws of logic.

3) Therefore, toast can account for laws of logic.

Obviously, the absence of toast cannot ‘account’ for anything, especially the notoriously murky metaphysics of logic. Does this mean though that toast itself can? It seems equally obvious that it cannot. Taking one out of the running is not all that is needed to show that the other is the winner by default. Neither toast nor ‘non-toast’ can account for the laws of logic. The unsoundness of the argument is painfully obvious when ‘toast’ is used in place of ‘God’.

In other words, (1b) is a false dichotomy for the same reason the following is a false dichotomy:

Either John murdered his wife because he wanted the insurance money, or not-because he wanted the insurance money. 

Obviously, there are other logical alternatives: it’s possible John didn’t murder his wife at all, or that nobody else murdered her either, or that he isn’t even married in the first place. Likewise, it’s possible that nothing needs to account for the laws of logic, or that nothing can account for the laws of logic, or that (depending on what we mean by them) the laws of logic don’t exist in the first place.

Now recall the structure of Matt’s argument:

    1. If we have only two possible options by which we can explain something and one of those options is removed, by default the other option is verified since it is impossible to negate both of the only two exist options.
    2. God either exists or does not exist. There is no third option.
    3. If the no-god position, atheism, clearly fails to account for The Laws of Logic from its perspective, then it is negated, and the other option is verified.
    4. Atheism cannot account for the necessary preconditions for intelligibility, namely, the existence of The Laws of Logic. Therefore, it is invalidated as a viable option for accounting for them and the only other option, God exists, is validated.

Matt is free to keep the false dichotomy in his argument (“Either God’s existence accounts for the laws of logic, or God’s nonexistence accounts for the laws of logic.”) but in doing so he forfeits the very feature he believes makes his argument irrefutable. Namely, the atheist is no longer forced to concede that if they cannot account for the laws of logic, God must exist by default. Since the dichotomy is a false one, the premise in which it appears can be rejected outright by any rational person.

Why does this matter? 

It matters because once the atheist (rightfully) rejects the premise in which Matt’s false dichotomy appears, the burden of proof shifts back where it belongs, onto Matt. Behold the presuppositionalist’s worst nightmare: the atheist may sit back with her arms folded and say, “Why should I think that if I can’t account for the laws of logic, God must exist?”

Matt’s usual recourse, “Because it’s the only other option,” is no longer available to him here. Rather, Matt now takes on the colossal task of demonstrating everything his argument was designed relieve him of having to demonstrate:

  • Laws of logic exist (which entails an account of what, exactly, they are).
  • Laws of logic are such that they can be accounted for.
  • Laws of logic are such that they need to be accounted for, etc.

Matt must, in one fell swoop, definitively answer questions that philosophers have pondered and debated for centuries. Best of luck to him.

So, how do we make it a “true” dichotomy?

The placement of the negation within the sentence matters. We could make (1b) a “true” dichotomy by moving the location of the “not”:

1c. Either it is the case that God’s existence accounts for the laws of logic, or it is not the case that God’s existence accounts for the laws of logic.

So what is the fatal problem with the “true dichotomy” version, then?

There are two problems, really. One is that this corrected premise does nothing to help Matt when we plug it back into the argument:

1b. Either it is the case that God’s existence accounts for the laws of logic, or it is not the case that God’s existence accounts for the laws of logic.

2b. It is not the case that [it is not the case that God’s existence accounts for the laws of logic].

3b. Therefore, it is the case that God’s existence accounts for the laws of logic.

Even if God’s existence accounts for the laws of logic (note that as yet, this has only ever been asserted by the presuppositionalist, never demonstrated), the argument now has nothing to say about whether anything else could or couldn’t account for the laws of logic, or whether God’s existence, while sufficient, is even necessary for such an account. Does God actually exist? We don’t know, because corrected thusly, this argument can’t tell us. 

The second problem is far worse, as it pertains to the logical structure of the argument itself. In his refutation, Alex clearly explains that any disjunctive syllogism which uses a genuine dichotomy (p or not-p) for its first premise will necessarily beg the question.

Remind me: what’s begging the question?

Begging the question is a formal logical fallacy in which the truth of the argument’s conclusion is assumed by the argument’s premises. An argument which begs the question has no force; it is the same as saying, “I’m right because I’m right”.

Okay, so how does the “true” dichotomy lead to that?

It should be clear to anyone who read Alex’s original refutation, but let’s go over it again. The form of the argument is this:

1. p or not-p
2. not [not-p]
3. Therefore, p

But “not [not-p]” is logically synonymous with “p”. So really, the argument is:

1. p or not-p
2. p
3. Therefore, p.

Obviously (1) is redundant here. It adds no propositional content that wasn’t already there. We can remove it from the argument, which now becomes:

1. p
2. Therefore, p.

In other words: “I’m right because I’m right”. It doesn’t matter what sentence “p” stands for:

1. God exists.
2. Therefore, God exists.

1. God doesn’t exist.
2. Therefore, God doesn’t exist.

Any disjunctive syllogism with a genuine dichotomy as its first premise is trivial and useless.

What’s the TL;DR version of all this?

It’s simple. Matt Slick thinks that Alex Malpass’ criticism of his argument is merely a technical nitpick about phrasing, easily remedied. That’s wrong. What Alex has shown is that, as long as Matt’s argument takes the form of a disjunctive syllogism, there is no way to reword it or correct it so as to rescue it from failure. If the argument’s disjunction (its first premise) is allowed to remain a false dichotomy, then Matt forfeits the very feature of his argument that did all the heavy-lifting for him: “God exists” can no longer be inferred from the atheist’s (supposed or real) failure to account for the laws of logic. Alternatively, if the disjunction is corrected so as to be a genuine dichotomy, then the argument fails because it necessarily begs the question, a logical fallacy that renders the argument useless. Any which way, Matt’s TAG fails decisively. If he wishes to prove God’s existence, he must find a new argument.


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