The seventeenth century was a period of dramatic change in the field of philosophy. In logic, traditional Aristotelian textbooks were transformed by the emergence of an alternative ‘logic of ideas’. This new logic was developed by Descartes and Locke, its main representatives, and by Arnauld and Malebranche. The present study starts with a fresh and detailed analysis of the logic of ideas. The author then puts the fruitfulness of his characterization of the new logic to the test, by studying its reception in the eclectic intellectual environment of the Dutch Republic between 1690 and 1750. This is the first comprehensive study of the early modern logic of ideas. It is also a profound contribution to our understanding of the interaction between Aristotelianism and new philosophy and between rationalism and empiricism.