Over in Craig-Land recently there was a discussion as to why
WLC uses the modus tollens rather than the modus ponens in his moral argument. That is to say, why does he use the double negative
(specifically "if not god did not exist then objective moral values and
duties would not exist") rather than something more comprehensible (such
as "if objective moral values and duties exist then god exist"). I've touched on this before when I suggested that WLC
does this to confuse and distract. I
also suggested in The modified WLC moral proof that the argument,
structured as it is, can argue for the existence of god using anything you like
- even totally meaningless things such as Kim Kardashian:
1. If god did not exist, the Kim
Kardashian would not exist.
2. Kim Kardashian does exist.
3. Therefore god exists.
Amusingly, it would appear that WLC agrees.
As you can see, p → q comes out
false only when the antecedent clause is true and the consequent clause is
false. (I know that seems weird, but that’s the way “→” is understood
logically.)
So what does this imply for the first premise of the moral argument?
1. If God does not exist, objective moral values and duties do not exist.
Well, since God does exist, the antecedent clause is false. Therefore, no
matter what the consequent clause is, (1) comes out true! (Look at our truth
table above.) So it is also true that
1′. If God does not exist, objective moral values and duties do exist.
A falsehood implies anything! So for the theist, (1) and (1′) are said to be
trivially true or vacuously true.
Falsehoods imply anything.
So the false claim that god exists would, by extension, imply the
existence of "objective moral values and duties" as well as implying
the non-existence of "objective moral values and duties". The false claim that god exists would imply
the existence of Kim Kardashian as well as implying the non-existence of Kim
Kardashian.
Thank you, Dr Craig. Torpedoing
your own moral argument … well done.
---
That is not, by any stretch of the imagination the only problem
with that short text. WLC claims that
"p → q comes out false only when the antecedent clause is true and the
consequent clause is false", by which he means that if p is true and q is
false, then there is a problem with the claim that p → q.
Note that p → q is logical symbology for "if p, then q"
(and in some instances "p implies q" or "p necessitates q"). What WLC is saying is that this is a "false"
premise, if we have an instance in which we have p being true, and q not being
true. The claim that p → q doesn't say
anything about instances in which there is no p, or where p is false. Let's put this into words.
If Tiddles is a standard cat,
then Tiddles has four legs.
If we were to look at Tiddles, confirm that Tiddles is a
standard cat and yet find that Tiddles has five legs, then we would have cause to
mistrust our premise.
If on the other hand, we were to find that Tiddles is not
a standard cat, then we have no basis on which to argue anything. This premise is quite limited. It is not true to say that:
If Tiddles is not a
standard cat, then Tiddles has five legs.
We could look at Tiddles, observe that she is a standard
horse and then conclude that, despite not being a standard cat, she does in
fact have four legs. Or we could observe
that Tiddles is standard giant pink seastar and has what we could call five
legs. Not being a cat doesn't give us
much information about Tiddles.
But what WLC is telling us is that if p (in this case
"Tiddles is not a standard cat") is false, then no matter what q is,
then p → q will be true! No, no, no no
no.
That's not how it works.
The premise that "If Tiddles is a standard cat, then
Tiddles has four legs" is true irrespective of what Tiddles is. We just get to the first half of the premise
(the conditional), check whether it applies and, if it doesn't, we move one
thinking "this premise isn't relevant to the situation in which we find
ourselves".
If it certainly not true to claim that, if Tiddles is not a
standard cat that suddenly it would be true that, if things were otherwise and
Tiddles were a standard cat, that Tiddles would be a pony. It's nonsense and WLC should be ashamed to
have written this.
It's rather worrisome that someone who relies so
heavily on logic in his arguments, and who is responsible (to some extent) for
teaching logic, should be such a duffer when it comes to explaining something
as basic as how premises work.