 In the debate with Ryle which unfolded on the pages of Mind and in the private correspondence Collingwood had tried to defend the claim that there is a distinctive kind of proposition which captures the subject matter of philosophy, but his attempt to capture the distinctive subject matter of philosophical analysis was dismissed by Ryle as being of a piece with a dusty old metaphysics. The drastic change of terminology in An Essay on Metaphysics is at least in part an attempt to defend the claim that philosophy has a distinctive subject matter different from both that of the exact and the natural sciences, but to do so in a way that would not lend itself to the kind of misunderstanding that led Ryle to dismiss Collingwood’s metaphilosophical vision as belonging to an idealist metaphysics of the sort that analytic philosophy wanted to leave behind. This terminological change put Collingwood in a better position to engage with the revival of empiricism at the hands of A.J. Ayer. In Language Truth and Logic (1936) Ayer revitalised Hume’s critique of metaphysics by invoking the principle of verifiability, according to which propositions are meaningful insofar as they are empirically verifiable. Propositions which are not empirically verifiable are nonsense unless they are tautologies. As far as Collingwood was concerned Ayer’s revival of the Humean fork had unpalatable metaphilosophical implications because it entailed that to be meaningful the claims of philosophy must be either empirically verifiable, as the propositions of natural science, or analytic truths, as the propositions of exact science. An Essay on Metaphysics is a pointed attack on the metaphilosophical implications of this claim. Ayer’s commitment to the view that there are only two types of legitimate propositions, empirical and analytic, was, for Collingwood, based on a failure to acknowledge that statements can play different roles in the logic of question and answer. Some statements are answers to questions and, in so far as their role is to answer questions, they are truth evaluable. But some statements have a different role, namely, to give rise to questions and they perform this role not in so far as they are true or false, but in so far as they are presupposed. As such they are not truth evaluable, because they are not asserted as propositional answers to questions. Statements such as “a cause is an event by producing or preventing which one can produce or prevent that whose cause it is said to be” (sense II of causation) is not asserted by the philosopher as a proposition. What the philosopher asserts is not “causes in sense II exist or are true of an inquiry independent reality” (which would be an illegitimate metaphysical proposition) but rather “causes in sense II are absolutely presupposed in the practical sciences of nature”. Philosophy yields not first order knowledge but second order knowledge or understanding of the presuppositions on which knowledge rests. Ayer’s classification of propositions along the lines of the Human fork conflates presuppositions with propositions and, as a result, fails to acknowledge that philosophy has a distinctive subject matter, namely absolute presuppositions, and a distinctive role, to detect presuppositions. Absolute presuppositions are not reducible either to the propositions of the exact or those of the natural sciences. Nor are they ruled out as meaningless propositions by the principle of verifiability because, since they are not propositions, the notion of verifiability does not apply to them.