For those unfamiliar with Dr. Craig's work, he often uses deductive arguments when making his case for theism. He is an avid defender of the Kalam and Leibnizian cosmological arguments, the fine-tuning argument and the moral argument.
In his article The New Atheism and and Five Arguments for God, Dr. Craig explains what makes a good deductive argument:
"An argument is a series of statements (called premises) leading to a conclusion. A sound argument must meet two conditions: (1) it is logically valid (i.e., its conclusion follows from the premises by the rules of logic), and (2) its premises are true. If an argument is sound, then the truth of the conclusion follows necessarily from the premises. But to be a good argument, it’s not enough that an argument be sound. We also need to have some reason to think that the premises are true. A logically valid argument that has, wholly unbeknownst to us, true premises isn’t a good argument for the conclusion. The premises have to have some degree of justification or warrant for us in order for a sound argument to be a good one. But how much warrant? The premises surely don’t need to be known to be true with certainty (we know almost nothing to be true with certainty!). Perhaps we should say that for an argument to be a good one the premises need to be probably true in light of the evidence. I think that’s fair, though sometimes probabilities are difficult to quantify. Another way of putting this is that a good argument is a sound argument in which the premises are more plausible in light of the evidence than their opposites. You should compare the premise and its negation and believe whichever one is more plausibly true in light of the evidence. A good argument will be a sound argument whose premises are more plausible than their negations."1
As Dr. Craig notes, the power of arguing this way is that if a deductive argument is sound, the truth of the conclusion follows necessarily, whether you like the conclusion or not. Deductive arguments are a standard way of arguing. Which is why Dr. Krauss's strange attack on deductive arguments during this dialogue was so bizarre.
In his speech, Dr. Krauss warned the audience that they need to beware of syllogisms because they can lead to false conclusions. He offered the following example:
1. All mammals exhibit homosexual behavior.
2. William Lane Craig is a mammal.
3. Therefore, William Lane Craig exhibits homosexual behavior.2
As you can imagine, the audience got quite a chuckle from Krauss's argument! However, I fear that some missed the error in Krauss's sad attempt to undermine deductive arguments. There are two problems with Dr. Krauss's "homosexual mammal" argument: 1) It is self-defeating to use logic to refute logic 2) this argument is informally invalid because it uses terms equivocally. Dr. Craig explains:
"It’s like the following syllogism, Kevin: Socrates was Greek; Greek is a language; therefore Socrates was a language. Now that’s obviously wrong because it uses the word “Greek” equivocally. In the first premise it’s an ethnicity, in the second premise it’s a language. And so the argument is simply invalid because of equivocation. Similarly, when you say: all mammals exhibit homosexual behavior, what you mean is: all species of mammals. But when you say in the second premise: William Lane Craig is a mammal, you don’t mean William Craig is a species of mammal, you mean he is an individual organism that is a mammal. And therefore the argument is invalid; you’ve used the terms equivocally. If you mean, all individual organisms that are mammals exhibit homosexual behavior then the first premise is false. If you mean, by the second premise, William Lane Craig is a species of mammal then the second premise is false. So you cannot construct a valid argument from those premises when you use the terms to have the same meaning. It’s only by equivocating on the terms that you construct this argument leading to this false conclusion. So this, as I say, is really, oh, this is the low point of these three dialogues where Professor Krauss mounts this attack upon deductive logic itself based upon this specious argument."3
So, because of the self-defeating venture of using logic to refute logic and the fallacy of equivocation, Lawrence Krauss's bizarre attack on deductive arguments fails.
Further, if offers us a great illustration of why it is so important for the scientist to understand philosophy.
Courage and Godspeed,
Chad
1. William Lane Craig, The New Atheism and Five Arguments for God, 2010.
2. William Lane Craig and Kevin Harris, Reasonable Faith Podcast Transcript, "The Debate in Melbourne Part 2," Nov. 11, 2013
3. Ibid.
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