All of Sblast's Comments + Replies

What is unbelief?

Huh? Unless you are quoting from a fantasy story with an unusual magic system then I have no idea what you are talking about.

No. He's saying "if evolution shapes cognition this is what we would expect. Oh, hey, look! We see that." Incidentally, I suspect that even you don't think that evolution and cognition are completely unrelated. Different species are in different niches with different degrees of intelligence, and there's a heavy correlation between what sort of niche a species is in and how intelligent it is. Thus for example, omnivores are generally more intelligent than other species of similar size.

That assumption follows pretty straightforwardly from evolution and some trivial observations. If I meet a human, I expect with high likelihood that they will have cognitive capabilities in the ballpark with mine. If I meet a lobster, tree, or rock, then I expect with high likelihood that they will not have such cognitive capabilities. I assume that relationship is based on the way the thing is constructed. Or am I misunderstanding you?

There have been others explaining why "If P, then Q. Q. Therefore, P." isn't what is going on here, and why postdictions are not so bad. But I'd like to address another issue: there are a lot of historical examples where all the major evidence for a hypothesis was a postdiction, but the hypothesis was so simple and fit the data so well that it became accepted mainly on the power of the postdictions. The most famous example was Kepler's model of the solar system using ellipses. Based to a large extent on their postdictive power, the basic elliptical model was largely accepted before Newton gave an explanation for why it worked. This example isn't perfect because the model did provide further confirmation by later astronomical observations.

That would be a logical fallacy. But, importantly, its probabilistic analogue is not a fallacy. It really is a mathematical fact that, In other words, it is a mathematical fact that p(Q|P) > p(Q) implies p(P|Q) > p(P). I agree with you that predictions are better than postdictions in practice, but postdictions ain't nothing. First, see my final parenthetical remark in my previous comment. We already have causal accounts of why people die around 80. Alternative causal accounts (such as aliens) don't get much of a probability boost from explaining what we can already explain. In contrast, no competing theory predicts the "three brothers but not one" numbers specifically. If observations bore this out, the EvPysch explanation would not be competing with any alternative explanations. Second, recall that I said that, when a theory says that an observation is likely, and the observation actually happens, then That is true. Nonetheless, if T started out as very, very improbable, then even an increase by a "very large factor" will still leave T with a small probability. If epsilon is sufficiently small, then epsilon x 10^100 is still very small. Now, "Aliens kill people around age 80", starts out with a very low prior probability. So it will have to predict/postdict some very improbable observations to rise above a negligible probability. Third, and most importantly, simply adding an improbable observation to a theory lowers the prior probability of that theory. Take the theory "Aliens kill people". Now augment the theory by adding the "around age 80" part to get "Aliens kill people around age 80". This addition lowers the probability of the theory. (Under the original theory, the aliens could be killing people at any age. Thus, the original theory would be true under a wider variety of circumstances, so it is more probable.) In fact you can prove that the addition of "around age 80" exactly counteracts the boost that the augmented theory gets for successfully post-d

While propositional logic may be a special case of Bayesian reasoning, the Bayes's theorem formalization of the scientific method cannot be usefully reduced to propositional logic. Also, welcome to Less Wrong!. It sounds like you may want to check out Bayes' Theorem and/or Technical Explanation.

Actually, it's: If P, then Q is plausible. Q. Therefore P is plausible. And it's a valid argument in probability theory as extended logic; see the first chapter of Probability Theory: The Logic of Science, which is available on the linked webpage.

You are right that the "three brothers but not one" bit is detailed. That is why observing such specific numbers would provide strong support for the theory, even if you didn't "determine the actual cause from all the other possible ones". Mere observation is enough. That is the essence of Bayesian epistemology. In general, suppose that a theory T says that a highly-specific (and hence a priori improbable) observation E is likely, and then E is actually observed. Then that observation makes the probability of T increase by a very large factor. And the probability of T increases more, the more specific E is. In symbols, if p(E) is small, but p(E|T) is large, then the ratio p(T|E) / p(T) is very large. This is a direct corollary of Bayes's theorem: p(T|E) = p(T) * p(E|T) / p(E). Note that this applies even if you merely observed E, but didn't determine what caused E to happen. (However, if you subsequently did determine what caused E, and that cause differed from what T said it would be, then T would lose whatever favored status it had gained.)

What about the prediction that people would (statistically) sacrifice themselves for three brothers but not one, or for nine cousins but not three? Would this qualify, provided that these specific numbers were empirically observed? After all, no competing theory makes such precise numerical predictions, to my knowledge. So, if observations were to bear out these numbers, then that would provide strong Bayesian evidence for the evolutionary origins of this kind of altruism. Also, some of the things that you're calling "postdictions" are not universally acknowledged to be facts — e.g., claims about psychological differences between men and women. So, to the extent that convincing empirical evidence for these differences ultimately arises, wouldn't that qualify as an honest prediction of evolutionary psychology?