That’s from ‘How We Reason: A view from Psychology’ in The Reasoner 2(3), 4–5. Philip Johnson-Laird’s book ‘How We Reason’ is out in paperback next month.*......Either Jane is kneeling by the fire and she is looking at the TV, or else Mark is standing at the window and he is peering into the garden.Does it follow that she is looking at the TV?
*......Jane is kneeling by the fire.
......Most individuals say, “yes”, see Walsh, C., and Johnson-Laird, P.N. (2004: Co-reference and reasoning. Memory & Cognition, 32, 96–106). Given the first premise, they think of two possibilities: in one, the first conjunction is true; and in the other, the second conjunction is true. They overlook that when the second conjunction is true, the first conjunction is false, and that one way in which it can be false is when only its first clause is true, i.e., Jane is kneeling by the fire but not looking at the TV. Hence, the correct answer to the question is: “no”.
......Maybe that was an example of a fallacy, rather than a paradox, but I’ve labelled it under ‘paradox’ in view of how easy it is to see through those I’ve been looking at recently; and after all, I’d said “yes” myself. (There’s a nice list of fallacies in The Reasoner 2(5), 7–8.)