  The negative side of Gassendi's theory of knowledge bows in the direction of the classical Skeptics: we cannot be conclusively certain about, nor find ultimate truths among, empirical beliefs. The positive side rejects an absolute Skeptical doubt, however, suggesting that empirical knowledge is possible because we can identify a range of strengths that are normally associated with many beliefs about appearances—their reliability, approximation to the truth, and likelihood by degrees. This approach—what Popkin calls the via media of Gassendi, the ‘constructive’ skepticist—suggests a practicable if approximate understanding of the world is within our grasp.