 Although this performance is impressive, there is still a long way to go in training nets that can process a language like English. Furthermore, doubts have been raised about the significance of Elman’s results. For example, Marcus (1998, 2001) argues that Elman’s nets are not able to generalize this performance to sentences formed from a novel vocabulary. This, he claims, is a sign that connectionist models merely associate instances, and are unable to truly master abstract rules. On the other hand, Phillips (2002) argues that classical architectures are no better off in this respect. The purported inability of connectionist models to generalize performance in this way has become an important theme in the systematicity debate. (See Section 7 below.)