Rats were placed in situations pitting three motivations against each other. Two motivations, ambient temperature and need of water, were physiological drives. The third, water sweetness provided by sodium saccharin, was not considered as immediately physiological because saccharin does not provide physiological benefits for the animals; nevertheless they continued to seek the sweet taste after repeated exposure to it. Therefore, our aim was to explore whether these motivations are of the same nature for rats and, if they are, whether they are also quantitatively comparable. From the behavioral evidence we wanted to obtain information on the common currency that permits the rats to solve conflicts. Our results confirm the existence of a common currency in rats' motivations. The similarity of rats' behavior to that of humans observed in conflict situations, where maximizing the bidimensional sum of pleasure was the key to optimal behavior, allows us to suggest a role for affectivity in decision making of mammals.