Both of these are from Ernest Adams’ “A Primer on Probability Logic”, which I’m finding to be a nice, introductory level book with lots of examples I’ll be using in my Principles of Reasoning course next semester to compare deductive and probabilistic reasoning. Since the first has a pretty straightforward solution and the second lends itself to a somewhat more complex but well understood analysis, I’m not sure about labeling these “paradoxes”, but perhaps the difference between a paradox and a puzzle is purely psychological; i.e., a puzzle is a paradox only when the wrong answer is gripping, which is a subjective matter. So, different individuals will find these more or less paradoxical.
The first, “Simpson’s Paradox”, is given as a homework problem. Quoting Adams (p. 62):
During the 1985 baseball season Steve Sax of the Los Angeles Dodgers outhit Ron Oester of the Cincinnati Reds both playing on grass (.257 for Sax and .225 for Oester) and playing on artificial turf (.333 for Sax and .323 for Oester), yet Sax’s overall batting average was lower than Oester’s (.279 for Sax and .295 for Oester).
What gives? How could Sax have done better both on grass and on turf but not better overall? Well reflect that both players hit much better on artificial turf than on natural grass. With that in mind, what stands out as different between Riverfront Stadium where Oester played half of his games and had roughly half of his at-bats vs Dodger Stadium where Sax played his home games? It didn’t take me long to find Simpson’s “paradox” not particularly paradoxical. However, in Adams’ framework basic, static “probability logic” is an extension of the standard propositional calculus. In place of truth-tables with0/1’s for each primitive proposition (i.e., a “world for each combination of truth assignments to the primitive propositions) Adams allows for probability distributions subject to the constraints of the Kolmogorov axioms (i.e., a world for each probability distribution). Working out what the primitive propositions should be for the Sax/Oester scenario and an assignment of probabilities that gives the corrrect answer is a nice exercise and nontrivial.
(Question: Is “trvial/nontrivial” also a psychological matter?)
The second paradox/puzzle is also given by Adams as an exersize (p. 69). Again, quoting Adams:
If each team in the World Series has a 50-50 chance of winning any given game, does it follow that the team that wins the final game of the Series has a 50% chance of winning that game? If not, why doesn’t this follow as a particular instance of the universal statement “each team in the World Series has a 50-50 chance of winning any given game”? And if it doesn’t folow, can you restate the universal statement so as to make it clear exactly what follows from it?
It took me a bit to see what the questions were driving at, so let me explain what I think the problem is through a slight restatement. Suppose the Cubs win the first 3 games of the series. There’s a 1/8 prior chance of that. Suppose further that all three games were very close, so that we have no reason to revise our belief that the teams are very evenly matched, just like we have no reason to revise our robust probability of 1/2 when three straight heads are flipped. Aside from personal joy unprecedented except by my wedding day, some things follow from this. There are four games left, any of which will be the last if the Cubs win it. The chance that they win one of the remaining four is thus one minus the chance that they lose them all: viz., 1 – 1/16. So it would seem that the chance that they win the final game, having won the first 3, is 15/16, but doesn’t this contradict the universal statement that they have a 50-50 (i.e., 1/2) chance of winning any given game, which was never contradicted and was in fact employed in the reasoning that lead to the value 15/16?
Adams asserts in a footnote that the puzzle, which I find a bit more paradoxical than Simpson’s Paradox, relates to the problem of “referential opacity”, discussed in detail by Quine and raised prior to that in Frege’s discussions of the informativity of identity statements and of apparent violations of Leibniz’s Law. The trouble, briefly, is that we cannot, it seems, infer (even leaving aside the complications of the fictional setting) as follows:
(1a) Lois Lane believes Superman is a hero
(2a) Superman = Clark Kent
(3a) Thus, Lois Lane believes that Clark Kent is a hero.
Call this “argument.a”. The term “believes” creates a “referentially opaque” context. Logicians have marked those contexts in which the simple substitution of coreferring terms does not preserve truth by the term “intensional” (with an “s”–not “intentional” with a “t”), to be contrasted with “extensional” contexts, in which substitution of coreferring term preserves truth-values. Propositional attitudes, like “believes”, “knows”, “desires”, etc., are paradigmatically intensional. Modal operators, like “possibly” and “necessarily”, are also taken by logicians to create intensional contexts.
Suppose, to my delight, that the Cubs in fact win the Series in game 4. We now have the antinomy between the following, “argument.b” and “argument.c”. Recall that we are given in my restatement of the problem that the probability of the Cubs winning any game is 1/2 and that they have won the first three:
(1b) The probability of the Cubs winning game 4 is 1/2 (by instantiation of the given).
(2b) Game 4 = the last game of the series.
(3b) The probability of the Cubs winning the last game is 1/2.
_______________________________________________
(1c) The probability the Cubs winning any given game is 1/2.
(2c) The probability that they win one of the remaining four is one minus the chance that they lose them all: i.e., 1 – 1/16.
(3c) So, the probability of the Cubs winning the last game is 15/16.
What gives? There are a number of ways to approach paradoxes of referential opacity. One approach, championed by Bertrand Russell, is to pay very close attention to “definite descriptions”. Those are terms formed by using the word “the”: viz., in our case “the last game”. Russell maintained that although these terms behave grammatically like genuine proper names, that the correct analysis of their truth conditions will show that they have a disguised quantificational structure. (See Russell’s treatment of the truth conditions for the sentence “The present King of France is bald.” for details). The standard descriptivist approach to paradoxes of referential opacity would restate (2b) in a way that shows this quantificational structure, which will transform it from a simple identity statement to one with an existential quantifier out front and thereby block the inference to (3b).
I don’t find that to be the most insightful analysis of this puzzle, however, even if it is logically adequate. For one, there’s a question whether the Russellian approach generalizes to cover all opacity puzzles, since some do not involve definite descriptions. Russellians have claimed that ordinary proper names actually function as disguised definite descriptions, a claim that many have found gives an implausible account of the semantics of ordinary names. But we are digressing already.
I think that the proper analysis of this puzzle is in fact rather simpler. The puzzle arises from static logical reasoning. That is, in argument.b the information given in premise (2b) should allow a rational person to revise the belief expressed by (1b). On a good dynamical account of reasoing (1b) is abandoned upon learning that (2b) is true, provided all the background information that was given in the set-up of the puzzle. After all, if the Cubs have won the first three games and game 4 is the last game of the series then the probability that they win game 4 is not at all 1/2; it’s, in fact, 1! Oh, joyous day!!!!
There is, however, quite a bit more that could be said here about the relationship between descriptions and singular terms. What seems to be distinctive about descriptions, in contrast to singular terms, is that a when description is used to refer it does so in virtue of some piece of information about the referent. This is very important, given the requirement of total evidence, in probability contexts. If an entity is referred to using a description then our beliefs about that entity ought to be updated in light of that information. The same does not hold when a proper name is used to refer; we may have information associated with the name, but the name itself does not communicate any information in the way that a description does.