The human understanding is no dry light, but receives an infusion from the will and affections; whence proceed sciences which may be called "sciences as one would." For what a man had rather were true he more readily believes. Therefore he rejects difficult things from impatience of research; sober things, because they narrow hope; the deeper things of nature, from superstition; the light of experience, from arrogance and pride, lest his mind should seem to be occupied with things mean and transitory; things not commonly believed, out of deference to the opinion of the vulgar. Numberless, in short, are the ways, and sometimes imperceptible, in which the affections color and infect the understanding.
- Francis Bacon

1 Introduction

Starting already with Plato, philosophers have traditionally seen rationality and emotions as two distinctive, if not opposing concepts. The modern philosophy and the current research in neuroscience, however, show that emotions and rational though are closely interlinked. Relations of emotions and reason are now studied in different kinds of thinking, including decision making, legal inference, scientific investigation, and ethical deliberation. There are studies about the descriptive question of what role emotions play in the operations of our minds and about the normative question of what role they should play. 2 Definitions and Basic Problems

2.1 Rational Thought/Rationality

“Our supposed rationality is one of the most prized possessions of human beings and is often alleged to be what distinguishes us most from the rest of the animal creation.”

Rationality can be understood as a conscious normative concept providing us on every instance with one answer to the question of which action is to be chosen. No such positive definition has been yet achieved since there are often several competing actions regarded as rational. Nevertheless, positive characterizations of theoretical rationality have been proposed. Usually these are either (1) ‘beliefs that are either self-evident or derived from self-evident beliefs by a reliable procedure’ or (2) beliefs that are consistent with the overwhelming majority of one’s beliefs. Practical rationality, on the other hand, refers to actions that are maximally efficient in achieving one’s goals. The existence of rational thought is generally assigned to human beings, although some signs of rationality could be found also in dolphins and chimpanzees.