A comparative lawyer may claim that one of the functions of his discipline ought to be to provide a key to the conceptual presuppositions with which a lawyer from another system approaches a given subject; he may further claim that possession of this key is particularly useful in attempts at drafting international legislation, in which UNCITRAL has been engaged since its creation. It is true that at the international level, as at the national, the disagreements which are ultimately the most intractable are those relating to legislative policy. However, at the international level an identity of formulation may conceal a failure to agree on policy, and conversely, what appears to be a disagreement on policy may be no more than a difference in the choice of concepts. One must be on the lookout for superficial harmony which merely mutes a deeper discord and for verbal conflict which hides a fundamental identity of aim. In both cases the key lies in the conceptual presuppositions of each system or family of systems. The deeper discord escapes notice because the same formula means different things according to the framework in which it is read; the fundamental agreement on the end to be achieved is not seen because the conceptual routes which lead to that end are different.