  Pierre Gassendi (b. 1592, d. 1655) was a French philosopher, scientific chronicler, observer, and experimentalist, scholar of ancient texts and debates, and active participant in contemporary deliberations of the first half of the seventeenth century.  His significance in early modern thought has in recent years been rediscovered and explored, towards a better understanding of the dawn of modern empiricism, the mechanical philosophy, and relations of modern philosophy to ancient and medieval discussions. While Gassendi is perhaps best known in history of philosophy for his disputes with Descartes, his relations with other major figures, including Kepler, Galileo, Mersenne, Beeckman, and Hobbes, represented even more important transactions of ideas. And while Gassendi also sought to communicate anew the ideas of Epicurus, the Stoics, and other earlier thinkers, his resulting amalgam of perspectives provides a modern view of his own making, one of the touchstones of philosophy and science in his times: our access to knowledge of the natural world is dependent on the constraints and licenses that follow from our epistemic grasp being limited to information provided by senses.  Through this arch-empiricism—tempered by his priestly adherence to key elements of Church doctrine—Gassendi views metaphysics as a realm for speculation grounded in the possibility of empirical confirmation, logic as (by turns) a psychologistic and probabilistic enterprise, knowledge of the external world as built on and forever subject to sensory-based evidence, and ethics in quasi-hedonist, possibly quantifiable terms. Gassendi's philosophy is a constant review of other sources, a thorough consideration of the landscape into which his own empiricism fits and represents an alternative to contrasting claims, past and present. What is sometimes thought of as eclecticism—particularly in the posthumous masterwork, the Syntagma Philosophicum—actually recasts philosophy as a fully-referenced scholarly enterprise, advancing historical styles and rhetorical modes in philosophical research and exposition. In these changes he matches even the magnitude of innovation that marks his atomist matter theory, empiricist perspectives, explorations and defenses of the new physics, objections to the Meditations, and refutations of contemporary Aristotelians and mystical thinkers. It has been argued—perhaps unfairly—that Gassendi's core ideas are better preserved through the medium of writings by Boyle, Locke, Huygens, and Newton. Yet his presentation of an empiricism, atomism, and new cosmology in historical and philosophical context greatly advanced the community of scholarship in his day, and represents what was then a fairly new model of research and exposition—still in philosophical use today.