An alternative to the standard theory that language learners always formulate the simplest rule to accommodate data is proposed. This new position states that the system of formulating rules and the generalizations made from it by children and adults in the stages of language learning needs to be more specific. The present theory excludes the use of transformational and all other context-sensitive rules and is limited to the use of context-free phrase structure rules. It accepts the "slash categories" of generalized phrase structure grammar but rejects the metarules that generalize across them, because they tend to lead to the same kind of overgeneralization that a transformation leads to. A rule schema that allows rules to be added to the child's system as he learns them, by collapsing slash rules, explains piecemeal language learning and the adjustment of rules to new data presented to the child. Although problems remain in the theory, it holds promise as a basis for research into innate language acquisition and linguistic knowledge. (MSE)