 On to counterfactuals or subjunctive conditionals—conditionals of the form, “If it were (had been) the case that \(A\), then it would be (have been) the case that \(B\)”. A common treatment, due to Stalnaker (1968) and Lewis (1973), analyses them in terms of possible worlds. In a simple version, they are true just in case at the closest worlds where \(A\) is true, \(B\) is true, where closeness is understood as similarity in relevant respects. “If Kangaroos had no tails, they would topple over” is true when, at all worlds where kangaroos have no tails and which are as relevantly similar as it gets to the actual world, kangaroos topple over.