.
>> Remember, in unit four, one of the ways
that we discussed to refute an argument is
to show that it's invalid by using
parallel reasoning.
And, I want to give an illustration right
now of how an argument can be refuted by
means of parallel reasoning.
And the target of my refutation is going
to be the fascinating argument, gay sex
human nature and benefits, submitted by
Matthew Ivan Bennett.
And I should insist, before going on to
refute this argument by parallel
reasoning, that the conclusion of
Bennett's argument may very well, for all
I say here, be true.
My only point, is that whether or not the
conclusion is true, the argument itself is
not valid.
And let me illustrate that point right
now.
Here's how the argument goes.
Premise one, the simplest definition of
nature is the universe with all of its
phenomena.
Premise two, the simplest definition of
human nature is, therefore, the phenomena
of being human.
Premise three, a phenomenon of being human
is seeking the satisfaction of mutually
beneficial goals through sex, such as
comfort and bonding.
Premise four, not all sex is reproductive.
Premise five, so human nature allows
non-reproductive purposeful beneficial
sex.
Premise six, gay sex, although it is non
reproductive, can often benefit those who
practice it through comfort and bonding.
Conclusion, therefore, gay sex is often
beneficial in a way that accords with
human nature.
Okay, that's Benton's argument.
And as I said, the conclusion of that
argument may very well be true.
But now, let me try to refute that
argument by dint of parallel reasoning.
So consider the following argument.
One phenomenon of being human is seeking
easy, and affordable sources of nutriment,
finding nutrition in ways that are not too
expensive to obtain or consume.
Premise two, not all nutrition is farmed.
Right?
There's plenty of nutrition that we get
that's not farmed.
Eating berries off of the bush, eating
animals that we've hunted in the wild.
Premise three, so human nature allows for
the consumption of non-farmed, wild,
easily obtainable nutriment.
Premise four, eating senile people, though
they're not farmed, is a way of obtaining
nutrient that's very easy, that's very
affordable, and in fact, avoids the
draining on social resources that is
created by senescence.
Conclusion, eating senile people often
accords with human nature in a way that's
beneficial.
Now, I hope none of you are convinced by
my second argument.
Although it's true that all the premises
of the second argument are correct, I
don't believe that the conclusion is
correct.
I'm quite certain that the conclusion is
not correct.
If human nature means anything, if human
nature rules out anything, then it rules
out eating senile people.
But, if the conclusion of that argument is
not correct, even though the premises are
correct, what that shows is that the
second argument, the argument that I just
constructed, is not valid.
Its premises might all be true, but it's
conclusion is false.
And so the argument can't be valid.
Now, let's go back to Matthew Benton's
argument.
Benton's premises might all be true.
And his conclusion might also be true.
But even if his premises and his
conclusion are true, that doesn't show
that the argument is valid.
Of course, you can have an invalid
argument whose premises and conclusion are
all true.
And what I've attempted to do by
constructing a parallel argument is to
show that whatever the truth of Benton's
premises and his conclusion, the argument
that he's built is not valid.
It follows the same rule as the argument
that I constructed.
Well, if it follows the same rule, then
the two arguments are both either valid or
they're both not valid.
Since my argument is clearly not valid, I
conclude that his argument must not be
valid either, whether or not its premises
and its conclusion are true.
That's an example of refutation by
parallel reasoning.