Abstract
<jats:p>Within generative grammar, syntactic change is viewed as a process of parameter resetting once a generation of learners converges on a different parametric value from the one attested in adult grammars. Certain types of morphosyntactic changes, such as grammaticalization, are argued to give rise to structural simplification to the extent that they eliminate features associated with a given head. As a result, certain exponents of a feature F are introduced by external as opposed to internal merge (EM over IM). Simplicity requirements of this sort are viewed as general principles or strategies that guide the learner in the process of parameter setting and are third factor principles (along with UG and experience). The elimination of feature syncretisms (via loss of movement, reduction of a phrase to a head or affix, etc.) is based on the preference for external merge. However, this view seems to contradict the idea that internal merge (IM) is less costly than external merge given that it eliminates the search space in the derivation. Thus, under economy, IM (movement) should always be preferred. The reconciliation between the two perspectives comes from the fact that different economy considerations apply at different levels. The preference for IM over EM applies in the derivational component, while the preference for EM over IM has to do with the output of the derivation and applies at the externalization component. Any tension created between the two can give rise to opacity or ambiguity in the input triggering innovative settings for the learner.</jats:p>