A major challenge for Dual Process Theories of reasoning is to predict the circumstances under which intuitive answers reached on the basis of Type 1 processing are kept or discarded in favour of analytic, Type 2 processing (Thompson 2009 ). We propose that a key determinant of the probability that Type 2 processes intervene is the affective response that accompanies Type 1 processing. This affective response arises from the fluency with which the initial answer is produced, such that fluently produced answers give rise to a strong feeling of rightness. This feeling of rightness, in turn, determines the extent and probability with which Type 2 processes will be engaged. Because many of the intuitions produced by Type 1 processes are fluent, it is common for them to be accompanied by a strong sense of rightness. However, because fluency is poorly calibrated to objective difficulty, confidently held intuitions may form the basis of poor quality decisions.