 However, Hazen (1993: 141–2) has pointed out that Lewis’s objection violates essential type-restrictions. Classes of different levels belong to different logical types, just as concepts of different levels do. So Lewis’s attempt to talk about all set-like entities in one fell swoop involves an attempt to quantify across different logical types. But this violates type restrictions in the same way as an attempt to quantify simultaneously over objects and concepts of all different levels. Although we can quantify over each level of classes, we can never quantify over all levels simultaneously.