On 28/04/2010 22:28, Steven Peterson wrote:
Hi Craig,
On Wed, Apr 28, 2010 at 2:53 PM,<[email protected]> wrote:
[Craig, previously]
[P1] Socrates is a man.
[P2] A man is mortal.
[C1] :.Socrates is mortal.
[Steve]
What is implicit and agreed upon in advance without needing to be
stated is a premise P3 that tells us that such premises like P1 and P2
when taken together ought to make us conclude the sorts of claim that
you have concluded. Without such an additional ought-premise your
conclusion would be unwarranted.
You're confusing inference rules with premises.
Antidote @
http://www.ditext.com/carroll/tortoise.html
The inference rule states that if each premise IS true, then the conclusion
also IS true. What you ought to conclude is an additional question.
What you ought to conclude is what the inference rules are
prescribing. Aren't rules sorts of "oughts"? What is a rule if not a
claim about what ought to be done under certain circumstances? In
other words, I don't think I'm confusing them. I think such rules
really ARE premises that are taken for granted with out stating them
as such. Rules are norms and "oughts" that must be presupposed to be
able to derive an is from other ises. I think this is what Horse was
saying earlier.
There are two ways of looking at this. No new "is" is being created
really as you are just substituting one example with another (using the
ISA rule):
Socrates isa [Man]
A [Man] isa Mortal
By substitution
Socrates isa Mortal
another way of looking at it in the slightly expanded form that Craig
suggests would be
If [it is true that]
Socrates is a man
And If [it is true that]
A man is Mortal
then
Socrates ought to be mortal
The tricky bit with this sort of logic (and why I've substituted ought
for is) is whether all men are mortal, as the complete set of men, past
present and future, of which man is an instance, has to be assumed!
Ah, the fun you can have with logic!!
Horse
--
Life should NOT be a journey to the grave with the intention of arriving safely in an
attractive and well preserved body, but to skid in sideways, chocolate in one hand, wine
in the other, body thoroughly used up, totally worn out and screaming "WOO HOO what
a ride!"... Hunter S Thompson
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