We show that revision by single sentences and multiple revision are, in general, mutually irreducible processes. The result is given for revision in base logics, a framework for studying revision in arbitrary classical logics for various notions of bases. Within this framework, we demonstrate that revision by single sentences can not be represented as multiple revision. The result employs general relational semantics for base revision. In combination with the well-known result that multiple revision cannot be reduced to sentence revision, we obtain that sentence revision and multiple revision are mutually irreducible.