Enforcing Grammatical Restrictiveness Can Help Resolve Structural Ambiguity*

Two major issues in formal language learnability are the problem of learning restrictive distributions (sometimes known as the “subset problem”), and the problem of structural ambiguity. While substantial progress has been made in addressing each of these problems in isolation, a complication can arise when a learner is faced with a learning situation that exhibits both problems. It is possible for the two problems to interact: allowing grammars of differing restrictiveness can complicate efforts to contend with structural ambiguity. The main result of this paper is a demonstration that a construction already proposed for learning restrictive grammars, the r-measure, can be used to contend with the complications in structural ambiguity that result from the existence of grammars of differing restrictiveness.