Counterfactual Dependencies
Kasper Højbjerg Christensen

Abstract:
This thesis is concerned with developing an adequate semantics for
counterfactual conditionals.
  A counterfactual conditional is standardly taken to be an expression
of the form ‘if it had been the case that ϕ, it would have been the
case that ψ’, where ϕ and ψ are sentences and ϕ furthermore expresses
something false. Now since expressions of this form are not
truth-functional in the standard sense, the task of coming up with an
adequate semantics for them has proven to be a somewhat difficult
affair. We will present some theories of counterfactuals and discuss
the problems that these have. Many of these theories agree that to
evaluate a counterfactual we need prior knowledge of certain
relationships in the world. We agree on this point, but we will
redefine what these relations are; namely generation relations where
we say that X and Y are in this relation when X will bring about Y ,
while remaining silent on whether Y will obtain when X does not.
  We incorporate this into a dynamic setting where the meaning of a
sentence is an operation on the cognitive state of an agent. We also
draw a distinction between a counterfactual being true in an absolute
sense and a counterfactual being acceptable by an agent. Throughout
the thesis we will concern ourselves mostly with the latter notion and
propose that if one believes in such a thing as the truth-value of a
counterfactual, then this is to be defined as acceptability by a
certain idealized agent.