You'd think so, except that the rest of the paragraph doesn't seem to make much sense if this is just a typo, does it? "X and therefore Y" and "X and X is the cause of Y" must both have smaller probability than "X", just like "X and Y". It seems to me that this is a thinko rather than a typo -- somebody really thought that the conjunction X&Y must have higher probability (like, it's X AND Y so it's probability is that of X PLUS the probability of Y, or something), while "X and therefore Y" must have lower probability than X. Or something.
Alternatively, perhaps someone felt that ranking "X and Y" interpreted as "X and therefore Y" as more probable than "X" could be interpreted as "the conditional probability of Y given X is higher than the probability of X"? But that seems like an extreme stretch of the words.
Reading the original source might clarify things [i.e., Hertwig, Benz and Krauss (2008)] -- unfortunately I don't have the time right now, anyone?
(BTW, I've always wondered whether, given that the conjunction is on the list as an "alternative" choice, subjects interpret "X" by itself as "X but not Y". I've always thought someone would have done experiments to test that idea, but I haven't looked into the literature deeply enough to know.)
(BTW, I've always wondered whether, given that the conjunction is on the list as an "alternative" choice, subjects interpret "X" by itself as "X but not Y". I've always thought someone would have done experiments to test that idea, but I haven't looked into the literature deeply enough to know.)
Actually, even though this explanation works for the oft-cited Linda case, it turns out that the locus classicus Kahneman & Tversky 1983 already contains several (versions of) experiments that yield conjunction-fallacy-type results but could not plausibly be interpreted in that way.
The chapter on judgment under uncertainty in the (excellent) new Oxford Handbook of Cognitive Psychology has a handy little section on recent critiques of the "heuristics and biases" tradition. It also discusses problems with the somewhat-competing "fast and frugal heuristics" school of thought, but for now let me just quote the section on heuristics and biases (pp. 608-609):
My thanks to MIRI intern Stephen Barnes for transcribing this text.