 The most similar \(\phi\)-worlds are in the innermost gray region. So, this analysis excludes any worlds from being in the shaded innermost blue region. Comparing Figures  4  and  5,  one difference stands out: the similarity analyses does not require that there be no \(\phi\land\neg\psi\)-worlds in any sphere, just in the innermost sphere. For example, world \(w_1\) does not prevent the counterfactual \(\phi &gt;\psi\) from being true. It is not in the \(\phi\)-sphere most similar to w. This is the key to semantically capturing the non-monotonic interpretation of antecedents. The truth of \(\mathsf{A &gt; C}\) does not guarantee the truth of \(\mathsf{(A\land B)&gt; C}\) precisely because the most similar \(\mathsf{A}\)-worlds may be in the innermost sphere, and the most similar \(\mathsf{A\land B}\) may be in an intermediate sphere, and include worlds like \(w_1\) where the consequent is false. In this sense, the domain of worlds quantified over by a similarity-based counterfactual varies across counterfactuals with different antecedents, though it does express a strict conditional over this varying domain. For this reason, D. Lewis (1973b) and many others call the similarity analysis a variably-strict analysis.