 The relative merits of these two restrictions are weighed by Tennant (2002). Tennant’s restriction is the less demanding of the two, since it bars only the substitution of those statements that are logically unknowable, and so, only those statements that are responsible for the paradoxes. Dummett’s restriction, by comparison, bars not only the substitution of these propositions, but also the substitution of logically complex proposition that are clearly knowable. Tennant also points out, if the knowability principle is the primary anti-realist motivation for revising classical logic, restricting that principle to basic statements can undermine arguments against a classical treatment of complex statements. 