  Yet Moore was not an uncritical follower of Russell. He was critical of Russell's account of implication in which Russell proposes that the truth-functional conditional expresses all there is to the logical relationship of implication between propositions, and introduced instead the term ‘entailment’ for this latter relationship (‘External and Internal Relations’ 90ff.). While recognising that entailment is closely connected to logical necessity he came to think that entailment is not just a matter of the necessity of the truth-functional conditional, thereby setting off a debate about this relationship which continues to this day. Again, Moore was critical of Russell's treatment of existence, in particular his denial that it makes sense to treat existence as a first-order predicate of particular objects (for Russell, existence has to be expressed by the existential quantifier and is therefore a second-order predicate of predicates). While agreeing with Russell that existence is not a straightforward first-order predicate (so that the logical form of ‘Tame tigers exist’ is not the same as that of ‘Tame tigers growl’), Moore argued that statements such as ‘This might not exist’ make perfectly good sense and that they could not do so unless the simpler statement ‘This exists’ also makes sense (‘Is Existence a Predicate?’ 145).