 Different accounts of logical consequence can be (and have been) formulated on the basis of (TP) and/or (ST): they can be viewed as both necessary but independent components of the notion of logical consequence, as Tarski seems to suggest in the passage above; they can also be viewed as closely related, in particular if (TP) can be reduced to (ST) (i.e. satisfaction of (ST) would entail satisfaction of (TP) and vice-versa) — a view that Etchemendy (1990) attributes to Tarski; or one may hold that the actual core of the notion of (logical) consequence is (TP), and that (ST) simply specifies a particular subclass of valid consequences, often referred to as formal consequences (Read 1994).