 A first important condition of adequacy on any reply to this problem is that scientific representations allow us to form hypotheses about their target systems. An X-ray picture provides information about the bones of the patient, and models allow investigators to discover features of the things models stands for. Every acceptable theory of scientific representation has to account for how reasoning conducted on representations can yield claims about their target systems. Swoyer (1991: 449) refers to this kind of representation-based thinking as “surrogative reasoning” and so we call this the Surrogative Reasoning  Condition.[2]  This condition distinguishes models from lexicographical and indexical representations, which do not allow for surrogative reasoning.