Note:
I am publicly apologizing for this post. In it I have taken Dr. Lawrence Krauss’ comment out of context. This was an honest mistake, as I was working from memory. When I wrote the post, I could not find the debate on You Tube to confirm the context in which he makes the statement below. After some readers had criticized me (and rightly so) for not having a link to the debate, I looked for it again. To my embarrassment, I found that Dr. Krauss’ was pointing out the need to be aware of wrong syllogisms, not pointing out how deductive reasoning is wrong. At the very end of the post I have included a link to the You Tube debate that I found after this post had been published for about 18 hours. Again, my apologies.
Dr. Lawrence Krauss Gets it Wrong….Again
In a recent debate in Melbourne, Australia between Dr. Lawrence Krauss (atheist, theoretical cosmologist and physicist, and author of A Universe from Nothing,) and Dr. William Lane Craig (Christian philosopher and apologist), Dr. Lawrence stated the following syllogism to show that deductive arguments don’t work:
“Look at this syllogism: All mammals exhibit homosexual behavior. William Craig is a mammal. Therefore, William Craig exhibits homosexual behavior.”
The syllogism is so outrages and provocative that people miss the point. The point is supposed to be that, here we have a valid argument based on true premises that leads to a false conclusion. It leads to the conclusion that William Craig is a homosexual; which is false. And yet that conclusion is derived from a valid argument with true premises. And therefore this is supposed to invalidate the use of deductive logic. This is astonishing.
Never mind the self-refuting procedure of trying to use logic to refute logic. The point is, this argument is informally invalid because it uses terms equivocally. It’s like the following syllogism:
“Socrates was Greek. Greek is a language. Therefore Socrates was a language.”
Now that is obviously wrong because it uses the word, “Greek” equivocally. In the first premise, it is 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 premises, “William Craig is a mammal,” you don’t mean William Craig is species of mammal. You mean he is an individual organism that is a mammal. And therefore, the argument is invalid. You have used the word 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 that, “William 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 is only by equivocating on the terms that you construct this argument leading to this false conclusion.
This was the most remarkable attack on deductive logic that I have ever heard. This was so bad. It represents the Marianas Trench of philosophy; it’s that low. It was the low point of these debates philosophically speaking.
Dr Krauss’ argument against deductive reasoning would have been equally true if he had said:
“Chairs have legs. I have legs. Therefore, I am a chair.”
or
“Cars have horns. Cows have horns. Therefore, a cow is a car.”
or
“A hog has a head. I have a head. Therefore, I am a hog.”
You see. It’s easy to do great logic!!
The problem is, we all know that Dr. Krauss is not a chair. But rather a cow is a chair.
++++++++++++++++++
Click here to watch the debate. Krauss’ statement starts at about 20 minutes into it.
Thanks for pointing this syllogism out, Mike.
I am astonished that a physicist would make so elementary an error in deductive reasoning. Do you know where he went to school?
You have done an excellent job of pointing out why his conclusion does not follow from his premises.
It is usually more helpful to have the second premise begin with the noun at the end of the first premise in order to keep things straight.
Your example, “Chairs have legs. I have legs. Therefore, I am a chair.” This could be more correctly phrased, “Chairs have legs. Legs have feet. Therefore, a chair has feet.”
Or another of your examples, “Cars have horns. Cows have horns. Therefore, a cow is a car.” Similarly, it would be correct to say, “Cars have horns. Horns make noise. Therefore, cars make noise.”
Diagrammed with letters, it becomes, “If A has B, and B has C, then A has C.”
The logic is thrown out the window if we say instead, “If A has B, and C has A, then C has B.”
This is what Dr. Krauss did.
It is little wonder he believes deductive arguments don’t work.
Ah, very good. Thanks for pointing that out to me. Now Krauss is a very respected physicist. In fact i just learned today that the wife of one of my cousins took physics from him while she attended Yale.
Corbin,
At the very top of the post, I have given a public apology because I took Dr. Krauss’ comment out of context. I have also attached a link to the debate on You Tube.
I enjoyed this one Michael! Speaking as a scientist…we do need a little watching 🙂
The reason Dr. Krauss went after deductive reasoning is because most of Dr. Craig’s arguments for the existence of God come from deductive reasoning. An example of one of Dr. Craig’s arguments would be:
Premise 1
Everything that comes into existence has a cause
Premis 2
The universe came into existence
Conclusion
Therefore, the universe has a cause.
As you will know, science does depend on deductive reasoning so this was just a weird argument for Dr. Krauss to make.
I suspect that Premise 1 here is false. I don’t think things “come into” existence. I think things are. Mormon theology teaches that, and the law of conservation of mass/energy, as well. Premise 2 is then only true in a narrow, equivocal sense. Reality is, physics doesn’t teach us anything so simple about God. Of course, I plan to address this sort of stuff in several of my future blog posts, although more indirectly. I hate these debates because no one attacks or defends the God I believe in, so they are nearly useless. Maybe I should start taking notes for a bigger discussion.
Melissa,
At the very top of the post, I have given a public apology because I took Dr. Krauss’ comment out of context. I have also attached a link to the debate on You Tube.
“Back of man! I’m a scientist.”
I think I meant “off.”
Of course Dr. Krauss isn’t a chair. Dr. Krauss only has two legs.
This article takes the quotes completely out of context, watch the video and back it up a few minutes before, Dr. Krauss is using this statement as an example to point out how illogical the argument being made by Craig is.
Profet,
You are correct. At the beginning of my post, you will now find an apology by me and at the very bottom, a link to the debate on You Tube.
Realmente, muito ridícula essa abordagem do Krauss, sofisma ateísta, é o que eles mais fazem. No meu tempo de ateísmo via Bertrand Russel dizer: ” Nada se cria do nada” o que era uma arma poderosa da argumentação ateísta em favor de um universo estático, ouvia de Nietszche: ” algo criar a si mesmo é auto contraditório”,e: “Se Deus está morto, tudo é permitido” e hj, se vê um ateísmo desesperado, que declara ser anti sobrenatural, mas defende um universo criado do nada, e ainda por cima q se auto recria inúmeras vezes, o que não é nada diferente de um milagre às escuras. Hoje o ateísmo é decadente, sem nenhum interesse pelas verdades, quer filosóficas, quer científicas. Se o Craig tivesse dito:
Nem todos os grupos de humanos são gays,
Krauss é um humano,
ele faz parte do grupo que não é gay:
Será que Krauss iria dizer que tal silogismo é mentiroso e falacioso?
Pobre ateísmo militante.