Assessment strategies for second language acquisition theories

There are numerous theories of second language acquisition (SLA), many of them oppositional. Whether or not this is inevitable now, culling will eventually be necessary if researchers are to meet their social responsibilities or if SLA is to be explained and a stage of normal science achieved. For the culling to be principled, a rational approach to theory assessment is needed, and the difficulty of identifying universally valid evaluation criteria makes this problematic. Assessment strategies used in other fields can be useful in SLA, but choice among them will depend on the researcher's (implicit or explicit) philosophy of science.