Author:
Wade A. Tisthammer
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Date Posted: 04/ 1/04 9:54am
In reply to:
Damoclese
's message, "Wade never admits, he slithers." on 03/31/04 2:55pm
First off, I do admit my mistakes, even as it pertains to Tristram Shandy arguments.
>>Why? Exactly how does the link bear any relevance to
>>anything I've said? I have explicitly and
>>repeatedly said that the argument being valid
>>merely means that the conclusion is true if the
>>premises are true, thus the only the argument
>>can fail is if one or more of its premises are
>>incorrect.
>
>You're wrong. Did you read the page?
>
>"1) It may be that the conclusion cannot possibly be
>false if the premises are true. If this is so, the
>argument is said to be formally valid (or deductively
>valid, or just valid). An argument may be formally
>valid and have one or more false premises, in which
>case the conclusion may also be false, or it may
>not.
You're wrong, did you read what I said?
From this post:
Valid just means that, if the premises are true, then the conclusion must be true also. A sound argument is one that is both valid and has all true premises. Is the argument valid? Yes, I've proved it. Is the argument sound? I don't have a formal proof for that, but if it isn't sound the only way the conclusion can be false is if one of the premises are false.
I never said anything to contradict the statement you bolded! I explicitly defined the difference between a valid argument and a sound one. Didn't you pay attention to what I said in my last post?
Yes, a valid argument can fail if one or more of its premises are false. But I've been claiming that all along. The entire point of me claiming that the argument is deductively valid is that the argument can fail only if one or more of its premises fail. Hence my often repeated question: which premise fails and why?
>An argument may be sound, and nonetheless fail to be
>convincing (if one does not believe the premises,
>despite their truth, or if it is a complicated
>argument and one does not understand how it follows,
>or trust that there is no mistake in it making it
>invalid). An argument may even be sound and fail to
>justify belief in the conclusion
I only partially agree with the last statement. In one sense it is clearly wrong. A deductively valid argument that is both valid and has all true premises necessarily means that the conclusion is correct. However, the argument can fail in the sense that it does not convince some people of the conclusion despite the fact that the conclusion is both correct and logically follows from the premises.
>Formally valid and yet still have a false premise
Yes. Now my question in regards to the Tristram Shandy argument: which premise fails and why?
I've discussed at length which premise
>(or implication or assumption however you wanna look
>at it) I think is baloney
Not really.
>namely the beginningless
>task.
What about a beginningless task? (Nowhere is it assumed that a beginningless task is even possible, for instance; in fact the argument seems to suggest the opposite.) What premise are you attacking? Why exactly does that particular premise fail?
>>What I'm saying is that if the argument fails,
>>a premise has to be wrong (because the argument is
>>deductively valid).
>
>You'd appear to be at odds with these fellows.
How so?
>They say something can be formally deductively valid, and
>still have false premises.
Damoclese, I've never said otherwise! If anything I have stated as much all this time. Why do you think I've been asking which premise fails and why? Why do you think I've been stating (repeatedly) that an argument being valid means that the conclusion is true if the premises are true? Why do you think I was asking you to attack a particular premise, claiming a failed premise was the only way the argument could fail to be sound? Once again I suspect overzealousness has clouded your perceptions.
>>Given this, exactly why should I make a full
>>retraction? A full retraction concerning what,
>>exactly?
>
>That my objection was a valid objection to the
>argument.
What would that be?
>That there needn't be "a premise"
>necessarily invalid, but that there is no reason to
>think these premises are true
I don't think I recall you ever saying that there is no reason to think these premises are true. Your objections as of late have been something like "There is no premise to support the idea of an infinite past to begin with," which is true but still irrelevant, since none of the premises are supposed to support the idea of an infinite past. If anything, they're supposed to do the opposite. Another objection is that the argument contains certain unwarranted assumptions, but for whatever reason refused to show me where those assumptions were made (i.e. in which premise) in the argument despite my requests.
In any case I disagree with the “no good reason to think these premises are true” statement. I have supported my premises, remember? I’ve demonstrated that if Tristram Shandy had been writing his autobiography in an infinite past (at the rate of one day per year) he is either infinitely far behind (in which case the present would never be reached) or he finishes at some point (and how can he possibly finish if it takes him an entire year to write one day?). Which premise do you believe is unsupported? Again, the only way the conclusion is to be wrong is to have one or more false premises. Which premise do you believe to be false?
>You're staring down a loaded gun here. You'd do well
>to back down and concede on this one.
Unless you're willing to give me some answers (e.g. which premise fails and why) you might want to check your ammunition again.
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