Sentence:  In recent years there has been increasing discussion of the "problem of <WSD>counterfactuals</WSD>". One way of formulating this problem is as follows: "What is meant when one asserts a conditional statement, the antecedent of which is contrary to fact?" 
Meaning of the word marked with <WSD> tags:  A conditional statement in which the conditional clause is false, as "If I had arrived on time . . .".<ref>"[http://www.philosophypages.com/dy/c9.htm#couf counterfactual]" in "A Dictionary of Philosophical Terms and Names" (Garth Kemerling, 1997-2002)</ref><ref>"Random House Webster's Unabridged Electronic Dictionary" (1987-1996)</ref>