This paper interprets Heidegger's frequently misunderstood criticisms of logic by presenting them in their historical context. To this end, it surveys the state of logic in the late 19th century and presents the main systematic conception of neo-Kantian logical idealism, noting Heidegger's own early involvement in these schools of thought. The paper goes on to present arguments from Heidegger's earliest lectures in which he develops both the phenomenology of everydayness and his criticisms of logic in an attempt to undermine the (...) neo-Kantian conception. These two approaches turn out to be inseparable in Heidegger's thought. Heidegger's criticism of logic amounts to a rejection of the claim that the possibility of experiencing objects is entirely grounded in logical constitution by the spontaneous understanding. There are other, more fundamental modes of disclosing objects. Heidegger is defended against the charge or irrationalism. The paper ends by interpreting the most important logic-related claims of What is Metaphysics? and outlining a Heideggerian response to Carnap's famous criticisms. (shrink)