In her chapter, Paola Basso examines Lambert’s attempt to solve the tension between the experimental and speculative dimensions of scientific knowledge by rejecting a strict dichotomy between experience and deduction. She argues that Lambert, defining philosophy as a science of qualities, aims to conjoin a Lockean-inspired anatomy of concepts with Wolff’s geometrical method. Basso analyzes Lambert’s understanding of the connection between observation and deduction as well as the ambivalent status he conferred to experience in his elaboration of the ‘golden mean’ on which scientific knowledge is founded. Based on this analysis, she argues that Lambert’s main contribution to epistemology consists in reconceiving the meaning of the a priori in order to account for a type of scientific cognition that combines an experimental basis with a priori deductions. According to this hybrid method, philosophy is to start with simple concepts obtained from experience and to proceed by developing what is contained in them through axioms and postulates, in the same way as geometry does for space.