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wedrifid comments on Undiscriminating Skepticism - Less Wrong
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Comments (1329)
Arguments from authority are invalid, but they are often inductively strong. If a community has a good track record for having good judgement within a given domain, then any particular judgement they make within that domain is evidence (sometimes weak, but sometimes strong) for the truth of their judgement. Arguably, scientists have relevant expertise in recognising what is and isn't science.
No they aren't. Incorrectly applied arguments from authority are often invalid but the form of argument is not itself intrinsically invalid. You do acknowledge this in your reasoning but I'd like to emphasize that the initial conclusion "Arguments from authority are invalid" isn't actually correct and that the 'inductive strength' makes the arguments valid when used correctly.
An argument is valid if and only if the truth of its premises entails the truth of its conclusion.
The truth of the premises of an argument from authority does not entail the truth of its conclusion.
Therefore, arguments from authority are not valid.
Note: This argument is valid in the sense I am using the term.
If your use of the term valid is such that arguments from authority are (necessarily) invalid then your use of the term is simply wrong. The very wikipedia link that you provide explains it as one of the many forms of potentially valid argument that is often used fallaciously. The following is an example of a valid argument form:
If you wish to trace the error in conclusion back to a specific false premise then it may be the (false) assumption "All valid arguments are deductive arguments".
That is indeed a valid argument-form, in basic classical logic. To illustrate this we can just change the labels to ones less likely to cause confusion:
The problem arises when instead of sticking a label on the set like "Snarfly" or "bulbous" or whatever you use a label such as "likely to be correct", and people start trying to pull meaning out of that label and apply it to the argument they've just heard. Classical logic, barring specific elaborations, just doesn't let you do that. Classical logic just wants you to treat each label as a meaningless and potentially interchangeable label.
In classical logic if you make up a set called "statements which are likely to be correct" then a statement is either a member of that set or it isn't. (Barring paradoxical scenarios). If it's a member of that set then it is always and forever a member of that set no matter what happens, and if it's not a member then it is always and forever not a member. This is totally counterintuitive because that label makes you want to think that objects should be able to pop in and out of that set as the evidence changes. This is why you have to be incredibly careful in parsing classical-logic arguments that use such labels because it's very easy to get confused about what is actually being claimed.
What's actually being claimed by that argument in classical logical terms is "Z is 'likely to be correct', and Z always will be 'likely to be correct', and this is an eternal feature of the universe". The argument for that conclusion is indeed valid, but once the conclusion is properly explicated it immediately becomes patently obvious that the second premise isn't true and hence the argument is unsound.
Where the parent is simply mistaken in my view is in presenting the above as an instance of the argument from authority. It's not, simply because the argument from authority as it's usually construed contains the second premise only in implicit form and reaches a more definite conclusion. The argument from authority in the sense that it's usually referred to just goes:
That is indeed an invalid argument.
You can turn it in to a valid argument by adding something like:
2a. Everything Person X says about Y is true.
...but then it wouldn't be the canonical appeal to authority any more.
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.
Thanks for applying Hanlon's razor.
Not only is it valid it is trivially so. It does not even rely on the possibility of there being valid inductive arguments. I made it the most simple of deductions from supplied premises.
Your problem here seems to be that you object to deducing a conclusion of 'likely to be' from a premise of 'likely to be'. By very nature of uncertain information things that are merely likely do not always occur and yet this does not make reasoning about likely things invalid so long as uncertainty is preserved correctly. (The premise could possibly be neatened up such that it includes a perfect technical explanation with ceritus paribus clauses, etc but the meaning seems to be clear as it stands.)
If the argument was in the form of a deduction when only an induction is possible from the information then the appeal to authority is invalid. If the argument is a carefully presented inductive claim then it most certainly can be valid.
Not all arguments are deductions. Not all arguments that are not deductions are invalid.
Jayson_Virissimo is talking about logical validity. The argument is not logically valid, because it is possible for "Z is likely to be correct" to be false, even if the other statements are true (for instance, add the premise "Z is incorrect"). Induction is not (in general) logically valid. It's valid in other senses, but not that one.
Yes, we both are. We have gone as far as to accept a shared definition of logical validity and trace the dispute from there.
This is simply false. The following premise:
... becomes invalid the moment there is in fact a "thing said <etc, etc>" that is not likely to be correct. That's why I put it there! It is an instance of the class of premise "ALL G ARE W" and so just like all other premises in that class it is false if there is a G that is NOT W. it just so happens that 'likelyhood' is the subject matter here.
The above serves to make the premise in question rather brittle. While it does means that the whole argument can be treated as deductive reasoning (about the subject of likelyhoods) it is also means that there are very few worlds for which that premise is true and meaningful.
I interpreted your premise as: (Things said about Y by a person who has a reputation for being an expert on Y) are likely to be (correct.) as opposed to (Things said about Y by a person who has a reputation for being an expert on Y) are (likely to be correct.)
If, as you seem to be agreeing, a thing cannot be "likely to be correct" and "incorrect" (as known by the same reasoner), then the premise reduces to "Things said about Y by a person who has a reputation for being an expert on Y are correct".
Is this really what you intended?
The second was the intended meaning.
Given the 'as known by the same reasoner' clause wouldn't that imply that it is '<...> cannot be known to be incorrect'? Either way it is clear that the encapsulation of the probabilistic parts is woefully inadequate here.
No, but it does seem to be the implication.
No it cannot.
That which is said to be invalid in the text that you link to (things such as generalizing from anecdotes to make mathematically certain claims about a set) is not the same kind of reasoning as that which we are talking about here. Here we are talking about probabilistic arguments, about which you say:
That leaves us at an impasse. There is not really much more I can say if you pit yourself against what is a foundational premise of this site: That the correct way to reason from evidence is to use Bayesian updating. You have essentially dismissed the vast majority of all useful reasoning as invalid. I disagree strongly.
The terms "valid" and "invalid" have a precise logical meaning; that is the meaning Jayson_Virissimo intends, as they have said many times now.
As you are using them, you seem to mean "well-grounded, justifiable, effective, appropriate, and etc."
Really this all could have been avoided if you all had just taboo'd the offending terms.
I have no problem parsing Jayson's claims. I would even repeat them if I wanted to guess the password of my highschool math teacher. However it is my assertion that the precise logical meaning has been applied incorrectly in this context. The problem is one of applying basic knowledge about logic without knowing enough about how to reason logically about probability.
That isn't actually the case.
I doubt tabooing the term "valid" would have helped. In my first reply to wedrifid I gave an explicit definition, a link to said definition (which includes citations), and an example. What more could you ask for?
You are correctly restating my claim. The vast majority of all useful reasoning is invalid. And by "invalid" I mean that it would not be self-contradictory to affirm the premises and deny the conclusion.
It is a straightforward matter to construct arguments based on probabilistic reasoning (and, by extension, arguments from authority) that adhere to that criteria. They go something like:
IF all evidence available indicates p(B|A) = 0.95
AND all other available evidence about B gives p(B) = 0.4
AND all evidence available indicates p(A) = 0.7
AND A
THEN available evidence indicates that the probability of B is slightly over 0.54
That argument is a simple and valid deduction (with an implied premise of 'rudimentary probability theory'). The conclusion cannot be (coherently) denied without denying a premise. This is what we are doing when we reason probabilistically ('we' referring to 'people while they are lesswrong thinking mode or something similar).
It may come as a shock to your philosophy tutor from freshman year but it actually is possible to reason logically about probabilities.
What? Of course it's valid (logically). The first three statements are premises and the final statement is the conclusion, which is entailed by the premises. If things said about Y by person X are likely to be correct and person X says Z about Y then Z is likely to be correct. That's a trivial deduction.
The argument is however not necessarily sound, because the premise "Things said about Y by a person who has a reputation for being an expert on Y are likely to be correct" is not universally true, for example if the person is saying stuff which blatantly contradicts other far stronger evidence.
Edit: Okay, enough silliness. Here is a formalised version of the above argument. You could run it through a proof checker, probably.
This argument is valid. It is not sound, because premise 2 is false. This is basic logic.
The link I provided (here) does not contain the string "valid" as of 01:43 1/22/2012 Phoenix, Arizona time. What is does say is:
Inductively Strong != Valid
That is more than a tad disingenuous. You seem to be trying to claim that because the string 'valid' is not present in the text the clear meaning of the text cannot be that arguments from authority can be valid. I hope you agree that this sounds silly if made explicit. Things that are present in article are the phrase 'statistical syllogism' and the inclusion of "Fallacious appeals to authority" as a whole seperate subsection. That section opens by explaining:
... This is an explanation of how fallacious arguments from authority differ from valid ones.
Yes, this is exactly my position.