Charles Morton was transatlantic Puritanism’s most famous educator at the time of his arrival in Boston in 1686. His Logick System advocated the vigorous Aristotelian logic popularized by Melanchthon. William Brattle, a generation younger than Morton, was one of Harvard’s most beloved tutors. Brattle introduced newly fashionable Cartesian logic into the Harvard curriculum. His Compendium of Logick ultimately superseded the text of his well known colleague and continued to be used at Harvard until the mid-eighteenth century. Although Harvard was a small provincial outpost in the history of logic, its position in America as a bastion of Puritanism makes it an excellent locale for the examination of one idiosyncratic strain of dogmatic, religiously-oriented logical thought. Morton’s and Brattle’s texts teach us much about the Puritans, especially about the epistemology, psychology, and theology that supported their particular form of religious rationalism.