 To this end, Kant introduces the idea of a “postulate,” defined as “a theoretical proposition, though one not demonstrable as such, insofar as it is attached inseparably to an a priori unconditionally valid practical law” (5:122). “These postulates are those of immortality, of freedom considered positively (as the causality of a being insofar as it belongs to the intelligible world), and of the existence of God”  (5:132).[19]  The law to which they “attach” is, of course, the moral law. It enjoins us to act for the sake of duty, with no assurances that anything will follow from this for our own happiness or that of  others.[20]  This creates a “dialectic” or conflict between happiness and morality. While morality is, for Kant, the sole unconditional good for human beings, he certainly does not deny that happiness is an important good, and indeed the natural and necessary end of every human being (cf. 4:415). This leads him to the concept of “the highest  good”:[21]