Department of Philosophy
PO Box 10 01 31, 33501 Bielefeld
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The meaning of conditionals is a matter of controversial discussion since antiquity. With respect to so-called subjunctive conditionals like (to use Adams' well-worn examples)
"If Oswald hadn't killed Kennedy, someone else would have." ,
David Lewis provided a (controversial) standard with his book Counterfactuals in 1973. With respect to so-called indicative conditionals like
"If Oswald didn't kill Kennedy, someone else did.",
however, there are still several theories under discussion. The proposals range from truth-functional approaches to approaches that deny that indicative conditionals have truth values.
In my thesis, I advocate a possible worlds semantics similar to Lewis' semantics for counterfactual conditionals according to which indicative conditionals have truth values but are not truth-functional. Thus, on the one hand, a possible worlds semantics for indicative conditionals has the advantage to evade classical problems for other approaches like the paradoxes of material implication. On the other hand, a possible worlds semantics for indicative conditionals yields, together with Lewis' theory of counterfactual conditionals, a uniform theory of conditionals.
Challenges for a possible worlds semantics are in particular: