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drethelin comments on Undiscriminating Skepticism - Less Wrong
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Comments (1329)
That argument is not valid. Valid arguments don't become invalid with the introduction of additional information, but the argument you provided does. For instance, compare these two arguments:
1.)
All men are mortal.
Socrates is a man.
Therefore, Socrates is mortal.
2.)
All men are mortal.
Socrates is a man.
Socrates is in extremely good health for his age.
Therefore, Socrates is mortal.
This argument will stay valid no matter how many additional premises we add (provided the premises do not contradict each other). Here is a variation of the argument you provided with additional information:
Person X has reputation for being an expert on Y.
Things said about Y by a person who has a reputation for being an expert on Y are likely to be correct.
Person X said Z about Y.
Person X said Z because he was paid $1,000,000 by person A.
Person X doesn't really believe Z.
Z is likely to be correct.
There is no contradiction between an argument having arbitrarily high inductive strength (like the very best arguments from authority) and still being invalid.
Probabilistic arguments are not the same as logical arguments. A Logical argument contains all information pertinent to the argument within itself. A probabilistic argument, by including words such as likely or probably, explicitly states that there is information to be had outside the argument. Probabilistic arguments are necessarily changed with the inclusion of more information.
Agreed. Probabilistic arguments are necessarily invalid (except when the probability of every relevant premise is equal to 1).
Is this an example of the persuasion tactic advocated (or described) recently? That is, you open with 'agreed' and then clearly say something that would undermine drethelin's whole comment.
No. I affirm all 4 sentences in drethelin's comment. Also, I maintain that nothing in drethelin's comment contradicts anything I have said in this discussion.
Really I just think he's using a stupidly strict definition of "Valid"
Yes, mathematical logic is "stupidly strict" with its definitions. It is designed that way.
I understand what you've been saying in this thread.
Unfortunately, mathematical logic is not a dialect often spoken in the comments section. Wiio's laws are totally in play, here.
Yeah, silly me. I should have provided a definition along with a link to a further elaboration of the concept so as to avoid any misunderstanding. Oh wait...
I again refer to the relevant reply. (And incidentally let it be known that I disapprove of snarkiness both here and elsewhere. Lack of understanding of that definition does not apply so the implied meaning of the snark is non sequitur.)
Thanks for applying Hanlon's razor.
So when a logician insists that only truth-preserving (deductive, not inductive) arguments are valid, he is demonstrating his stupidity?
Ah, that's too specific an interpretation of Hanlon's razor. The razor does not say that the malice and the stupidity need all come from the same party.
Fair enough.