When James of Venice translated the Posterior Analytics from Greek into Latin, in the second quarter of the twelfth century, European philosophy got one of the great shocks of its long history. John of Salisbury famously remarked that “it has nearly as many obstacles as it has chapters, if indeed there are not more obstacles than chapters” (Metalogicon IV.6). Latin philosophers had taken themselves to have a grip on Aristotle’s logic, but what they were discovering in the twelfth century was that their grasp extended only to what would be called the Old Logic, the ars vetus, leaving untouched the New Logic of the Topics, the Sophistical Refutations and, most importantly, the Prior and Posterior Analytics.Moreover, as the Latin philosophical canon swelled in the later twelfth century to include not just the full Aristotelian corpus but also the riches of Arabic philosophy, European authors realized just what a central role the Posterior Analytics in particular played in all this work. Although we now tend to focus on the recovery of Aristotle’s natural philosophy, metaphysics, and ethics, it is arguably the Posterior Analytics – not the Ethics, the Metaphysics, the Physics, or the De anima – that had the most pervasive influence on scholastic thought. For it is here that Aristotle sets out the methodological principles that are to be followed in the pursuit of systematic, scientific knowledge: what the Latin tradition would call scientia.