Talk:Raven paradox

black raven under doormat as a signal

Something should be added to the article regarding the argument Good (1967) made, that finding a black raven can count as evidence that "All ravens are black" is false, for example, if you and I have prearranged that, if discover "All ravens are black" to be false, then I will leave a black raven under your doormat to relay this information to you.

The section, "A false premise" above, discusses Good's argument. -- Derek Ross | Talk 00:37, 28 September 2009 (UTC)

There is something left out in the statement of the paradox

In addition to what I'm writing below, please see my comment above (just a couple of posts up) in response to the posting "Why just green apples?" The poster was correct in what he/she said. I cannot find anywhere in this article that the more general statement of the paradox is given.

I think something like the following should be integrated into the article:

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More generally speaking, the following it true:

The statement "For all x, if x is a raven, then x is black"

is, by elementary logic, equivalent to (see also my posting above):

"For all x, either x is not a raven or x is black". (The "or" here is the inclusive or.)

Therefore, the paradox can be stated: Every object you find that is either 1) black, or 2) NOT a raven, is evidence in support of the claim that all ravens are black. This is correct logic, but it clearly does not suggest a very fruitful way to conduct a scientific investigation.

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The point about the green apple in the introduction to the article is, it can be argued, incomplete. The green apple is both not-a-raven and it is not-black. My point is that BOTH of the following are evidence in support of the hypothesis that all ravens are black.

1) Finding a black apple (or a black raven or a black anything) and

2) Finding ANY thing of ANY color that is not a raven.

Of course, finding a non-black raven would disprove the hypothesis once and for all.

So, I'm suggesting this: The article needs to state that (R ==> B) <==> (~R or B). Again, please see my comment posted above under "Why just green apples?"

If no one has a legitimate objection, I will volunteer to add a comment to the article incorporating the above suggestion. I just wanted to post my suggestion in the discussion first, before making a change. Worldrimroamer (talk) 07:26, 17 December 2009 (UTC)

If you take a look at the earlier discussion you'll see that we have actually covered this point already. Make sure that you have read the prior discussions before adding anything to the article. -- Derek Ross | Talk 18:38, 17 December 2009 (UTC)

Thanks for the reply, Derek. You're right, if it's in the discussion I should (try to??) find it (if it doesn't get archived or something before I can read it). But the question still remains, at least in my mind: Why is the actual logically correct and complete statement of the "paradox" not in the article? I am stating neither personal opinion nor original research; I'm simply stating Aristotelian Logic 101. —Preceding unsigned comment added by Worldrimroamer (talk • contribs) 17:43, 19 December 2009 (UTC)

Understood. By all means add or expand upon the point if you feel that we haven't made it clearly enough in the article itself. I just meant that we'd already covered it on the discussion page. -- Derek Ross | Talk 18:27, 6 January 2010 (UTC)

thoughts

my informal and perhaps incoherent thoughts on the issue, just in case it sheds light on anything not already said:

in the statement that everyhing that is not a raven is not black, "everything" is not actually a closed set. for our purposes, it's a an unlimited open field. observing that the green apple is not a raven is (almost) equivalent to adding a new item to the set on the spot that is a non-black non-raven. if we added a non-black raven to the set on the spot, yes, that would be evidence (against), but we can't actually do that because ravens are defined as black. the statement is inductive, but once you start deriving other statements from it you lose track of its falculty of a non-definition. that's why it seems meaningless to introduce the evidence that a green apple, which is unrelated to ravens, is not black. it's unrelated to whether ravens are black by definition. (*actually, this isn't true.)

"i think it's true that all ravens are black"

if you translate that to "i think it's true that everything that is not a raven is not black", then maybe the green apple is actually evidence.

maybe the open question is whether "i think it's true that all ravens are black" is actually equivalent to "i think it's true that everything that is not a raven is not black." it's already been shown via other paradoxes that not all rules of deduction apply to belief statements.

a further ambiguity is that in "i thnik it's true that everything that is not a raven is not black" it is not clear whether we thnik that we may find a counterexample or that we think that everytihng that is not a raven is not black by definition. furthermore, saying that everything that is not a raven is not black doesn't tell us whether there is anything that is a raven or anything that is black. it also doesn't tell us if all ravens are black. it could be true that some ravens are white, but all non-ravens are also white. if everything is the collection of things in reality, tehre aren't necessarily black non-ravens. if everything is all possible imaginable things, then it includes black non-ravens, but observed things like a green apple are not evidence in that case. 74.186.83.219 (talk) 14:10, 6 January 2010 (UTC)

Thank you for your thoughts. Please take some time to read our policies on verifiability and original research. This is not meant to discourage you. If you have any questions, please don't hesitate to ask them here, on my page, or at the help desk. Happy editing, Paradoctor (talk) 17:12, 6 January 2010 (UTC)

(Probabilityislogic (talk) 04:27, 14 May 2011 (UTC)) I would add one (potentially) clarifying view, when you say "all ravens are black" you are basically saying the logical statement "R implies B", or that "R" and "R&B" have the same truth value (R is true if and only if R&B is true). Now this is not equivalent to "all non-ravens are non-black" (this is clearly false - a black cherry or black car or black anything serves as a counter-example to this statement). The equivalent reversal is "non-black means non-raven" or the logical statement "Not B implies Not R". Perhaps the paradox comes about from mistaking "Not R implies Not B" for the actually correct version "not B implies not R".

Picture

Does this page really need an illustration of objects that are not black and not ravens? If people are really in doubt that such objects exist they can temporarily look around the room they are in and find examples themselves. Also, why apples? —Preceding unsigned comment added by 82.6.96.22 (talk) 19:45, 5 May 2011 (UTC)

Paradox in popular culture

Would it be appropriate to add that Raven paradox is referred to in Episode 3 of the VN "Umineko no Naku Koro ni"? — Preceding unsigned comment added by 91.192.70.23 (talk) 11:44, 16 June 2011 (UTC)