The philosopher who flatly rejected 'man, the rational animal'

David Hume challenged the long philosophical tradition that defined humans as 'rational animals.' He argued that what we decide to do is always driven by desire and emotion, while reason merely calculates the means to satisfy those desires.

In his 'Treatise of Human Nature,' he wrote the provocative line that it is not contrary to reason to prefer the destruction of the whole world to the scratching of one's finger. Reason alone, he argued, can never tell us what to want — it only serves the desires that already exist.