In this book, I have developed and applied a theory of hypothetical thinking built around three key principles: singularity, relevance and satisficing. The processing model for this theory is a substantially revised version of the heuristic-analytic theory of reasoning that falls within the more general class of dual-process theories that have been widely applied in cognitive and social psychology. Processes described as heuristic (fast, parallel, implicit, high capacity) and analytic (slow, sequential, explicit, low capacity) in this theory map on to the distinction between System 1 and System 2 processing in the general family of dual-process theories (Evans, 2003; Stanovich, 1999). In the preceding chapters, the three principles and the role of dual-processes have been discussed in a wide range of cognitive tasks, including hypothesis testing, inductive reasoning, deductive reasoning, decision making and statistical inference.