 If metaphysical necessity is too coarse a notion to determine logical consequence (since it may be taken to render too many arguments deductively valid), an appeal to conceptual or analytic necessity might seem to be a better route. The trouble, as Quine argued, is that the distinction between analytic and synthetic (and similarly, conceptual and non-conceptual) truths is not as straightforward as we might have thought in the beginning of the 20th Century. (See the entry on the  analytic/synthetic distinction.)  Furthermore many arguments seem to be truth-preserving on the basis of analysis alone: