Philosophy
The Problem of Counterfactual Dependence in Causal Explanation
Quick fact
According to the counterfactual theory of causation, saying 'A caused B' implies that if A had not occurred, B would not have occurred either—a claim that is true in the closest possible worlds to ours.
Why this is interesting
Notice how you explain why a glass broke: 'Because the rock hit it.' But what if the rock hadn't hit it? Would the glass still have broken? That 'what if' is the heart of counterfactual dependence.
Read the full explanation
Understanding The Problem of Counterfactual Dependence in Causal Explanation
Imagine you're a detective investigating why a plant died. You see it wasn't watered, and you conclude the lack of watering caused the death. You're reasoning counterfactually: if the plant had been watered, it would have survived. This is the essence of counterfactual dependence: an effect depends on its cause in the sense that without the cause, the effect would be absent. Philosophers like David Lewis formalized this idea using possible worlds—ways the world could have been. To evaluate 'if not A, then not B', we look at the closest possible world where A doesn't happen and see if B still occurs. If B doesn't occur there, then B is counterfactually dependent on A. This dependence is what we often mean when we say A explains B: we're pointing to a counterfactual connection that grounds our causal explanation.
A deeper explanation
The mechanism behind this approach is the semantics of counterfactuals, developed by Lewis using possible worlds. A counterfactual of the form 'if it were the case that C, then it would be the case that E' is true if, in the closest possible world where C is true, E is also true. For causal explanation, the key is that C causes E if E is counterfactually dependent on C, that is, if in the closest world where C does not occur, E does not occur either. This makes causal claims objective: they don't rely merely on regularities we happen to observe, but on facts about how reality would have unfolded under different conditions. However, this raises problems: causal overdetermination (two rocks hit the glass, either would break it) and preemption (one rock hits, but the other would have if the first hadn't) break simple dependence. Hence, Lewis refined the theory to include chains of dependence. This shows that while counterfactual dependence captures much of our causal thinking, it must be handled carefully to account for all cases.