ABSTRACT
This chapter examines the principles in Newton's published work, both his Principia and his Opticks. It distinguishes between propositional-principles and ontic-principles. The chapter explains Newton's propositional-principles in their broader methodological context. It focuses on Newton's epistemic distinction between theories and hypotheses. The chapter shows that what differentiates Newton's principles from other kinds of theories is the function they serve—Newton's principles support his mathematico-experimental method in a crucial way. The inference structure of the Principia is roughly as follows: Newton started with his laws of motion. In a draft manuscript, originally intended as the preface to the Opticks, Newton wrote an account of principles. The manuscript presents a puzzle for the account of Newton's principles since this is the only place people find principles explicitly labelled as such. Newton contrasted the certainty of his own natural philosophical claims with the mere hypotheses and speculations which other philosophers found appealing.
