  The connectability condition brings with it a number of interpretive problems. Exactly what is, or should be, the status of the “suitable relations,” often called bridge “laws” or bridge hypotheses? Are they established by linguistic investigation alone? Are they factual discoveries? If the latter, what sort of necessity do they involve? Are they identity relations that are contingently necessary or will some sort of weaker relation, such as nomic coextensivity, suffice? Much of the philosophical literature on reduction addresses these questions about the status of the bridge  laws.[2]