Another solution to the problem of the meaning of theoretical terms is based on the rules of correspondence (also known as meaning postulates). They are statements in which observational and theoretical terms occur. Theoretical terms thus gain a partial interpretation by means of observational terms. Hempel raises two objections to this theory. First of all, he asserts that observational concepts do not exist. When a scientific theory introduces new theoretical terms, they are linked with other old theoretical terms that usually belong to another already consolidated scientific theory. Therefore the interpretation of new theoretical terms is not based on observational terms but it is given by other theoretical terms that, in a sense, are more familiar than the new ones. The second objection is about the conventional nature of rules of correspondence. A meaning postulate defines the meaning of a concept and therefore, from a logical point of view, it must be true. But every statement in a scientific theory is falsifiable, and thus there is not any scientific statement which is beyond the jurisdiction of the experience. So also a meaning postulate can be false; hence it is not conventional and thus it does not define the meaning of a concept but it is a genuine physical hypothesis. So meaning postulate do not exist.