 We might take the formal rules of logic to be totally neutral with respect to particular features of objects. Laws of logic, on this view, must abstract away from particular features of objects. Logic is formal in that it is totally general. One way to characterise what counts as a totally general notion is by way of permutations. Tarski proposed (1986) that an operation or predicate on a domain counted as general (or logical) if it was invariant under permutations of objects. (A permutation of a collection of objects assigns for each object a unique object in that collection, such that no object is assigned more than once. A permutation of \(\{a, b, c, d\}\) might, for example, assign \(b\) to \(a, d\) to \(b, c\) to \(c\) and \(a\) to \(d\).) A \(2\)-place predicate \(R\) is invariant under permutation if for any permutation \(p\), whenever \(Rxy\) holds, \(Rp(x)p(y)\) holds too. You can see that the identity relation is permutation invariant—if \(x = y\) then \(p(x) = p(y)\)—but the mother-of relation is not. We may have permutations \(p\) such that even though \(x\) is the mother of \(y\), \(p(x)\) is not the mother of \(p(y)\). We may use permutation to characterise logicality for more than predicates too: we may say that a one-place sentential connective ‘\(\bullet\)’ is permutation invariant if and only if, for all \(A\), \(p(\bullet A)\) is true if and only if \(\bullet p(A)\) is true. Defining this rigorously requires establishing how permutations operate on sentences, and this takes us beyond the scope of this article. Suffice to say, an operation such as negation passes the test of invariance, but an operation such as ‘JC believes that’ fails.