In the series of lectures that Peirce delivered at Harvard in spring 1865, given in revised form before the Lowell Institute in autumn 1866, we find the essentials of his early logical investigations. The lectures are for the major part devoted to the analysis of non-deductive forms of reasoning, i.e., induction and hypothesis. Besides the logic of mathematics, which rests upon the firm grounds of formal logic (roughly, syllogistic), Peirce shows that there is a logic of science, whose grounds of validity are to be investigated and evaluated. In Peirce’s terms, the main points of his lectures were “1st The degree and character of the certainty of scientific ratiocination. 2nd The degree and character of the certainty of scientific primitive principles” (W 1:162–163). The lectures contain penetrating discussions of Aristotle, the theory of syllogism, the conception of logic, the logic of probability, the theory of induction and of natural kinds, Boole’s algebra of logic, Mill’s doctrine of the uniformity of nature, the theory of the categories, the division of signs, and much else besides. Peirce’s father Benjamin attended the lectures and later wrote that he had been astonished “by the breadth, and depth and thought of his arguments, and his powers of research.” 1