Cue-based learners have often been proposed as models of language acquisition by linguists working within the Principles and Parameters framework. Drawing on a general theory of cue-based learners described in detail elsewhere (Bertolo et al., 1997), we show here that a recently proposed learning algorithm (Fodor's Structural Triggers Learner (1997)) is an instance of a cue-based learner and that it is therefore unable to learn systems of linguistic parameters that have been proved to be beyond the reach of any cue-based learner We demonstrate this analytically, by investigating the behavior of the STL on a linguistically plausible space of syntactic parameters.