 Third, the counterfactuals that are employed in the analysis are to be understood according to what Lewis calls the standard interpretation. There are several possible ways of interpreting counterfactuals; and some interpretations give rise to spurious non-causal dependences between events. For example, suppose that the events c and e are effects of a common cause d. It is tempting to reason that there must be a causal dependence between c and e by engaging in the following piece of counterfactual reasoning: if c had not occurred, then d would not have occurred; and if d had not occurred, e would not have occurred. But Lewis says the former counterfactual, which he calls a backtracking counterfactual, is not to be used in the assessment of causal dependence. The right counterfactuals to be used are non-backtracking counterfactuals that typically hold the past fixed up until the time (or just before the time) at which the counterfactual’s antecedent is supposed to obtain. Thus if c had not occurred, d – which in fact occurred before c – would have occurred anyway; so on the standard interpretation, where backtracking counterfactuals are false, the inference to the claim that e causally depends on c is blocked.