Induction and deduction, as discussed in the previous chapter, have received a great deal of attention from multiple quarters. In the ninteenth century, the philosophers William Whewell and Charles Sanders Peirce focused on retroduction as a distinct mode of reasoning. Retroduction had been recognized by Aristotle as a separate entity with specific properties; however, it wasn’t until Whewell and Peirce that a strong distinction between retroduction and induction was emphasized.1 Retroduction is an essential part of human reasoning, without which ideas of causal relationships essentially could not expand, as induction and deduction can only get one so far. Indeed, Peirce (who, it can be argued, was most instrumental in recognizing the role of retroduction in science) described this mode of reasoning as “the only logical operation which introduces any new idea and commented: “[N]ot the smallest advance can be made in knowledge beyond the stage of vacant staring, without making an abduction [retroduction] at every step.2”