This paper shows that Hume's theory of passion, such as elaborated mainly in book II of the Treatise of Human Nature (1739-40) and in the Dissertation on the Passions (1757), gives rise to a conception of the decision process which challenges the canonical approach to the rationality of decision, as rationality of preferences or rationality of choice. It shows that when adopting a Humean perspective, rationality is not embodied as consistency requirements of individual behaviour, but may emerge as a possible outcome of some dispositions of our mind, which make the world inhabited by our emotions.