Like the first myth of reason as the faculty that does away with the need for personal judgement, the second can also be traced back to Plato’s dialogues. In the Phaedrus, the soul is likened to a chariot pulled by two horses, one unruly and one of noble breeding. Intellect or reason is the charioteer, keeping troublesome emotion in line with the more obedient rational part of the self.
The metaphor reflects a historically common idea that although emotion can take charge if we let it, it is both desirable and possible to be guided by reason. It also reflects the related error of believing reason and emotion to be two autonomous drives. When these errors come face to face with the facts, they threaten to leave reason looking like an illusion. If we investigate how philosophers actually work, we find that they do not sit solely on Plato’s steeds of noble breeding but ride a more mongrel beast. And if we look at what psychology tells us about how the mind works, the idea of the rationalist thoroughbred seems as fanciful as the mythical unicorn.
By giving due consideration to the so-called irrational elements of thinking, we can revise our understanding of reason to show that while it does have an important role in guiding us through life, it does not and cannot do its work independently from the emotions and other psychological drives. To push the equine metaphor to breaking point, reason is no ass, but is more of a hard-working mule than a pedigree racer, and none the worse for that.