There is a controversy between two ethical viewpoints called internalism and externalism concerning desires and moral reasons. Internalism claims that it is logically impossible for an agent to have moral reasons without the agent's already existing desires for the actions required by these reasons Externalism claims that it is possible. We find a dilemma in this controversy such as : If externalist's claim is accepted, the relation between moral actions and moral reasons becomes unintelligible. For reasons alone cannot motivate actions. On the other hand, if internalist's claim is accepted, the morality lacks the supposed universality. For, desires are contingent. I think that dilemma can be solved in the following way. I assume that there is a moral value which is independent of agent's already existing desires. This value provides a justifying reason for a moral action. On the other hand, the recognition of this value by the agent generates a rational desire for this value, and therefore provides a motivating reason for doing the moral action in order to realize this value.