The Words-and-Rules theory is a relatively new development in the area of morphological productivity. This theory claims that irregulars are stored in the mental lexicon, while regulars are formed by a rule that attaches an affix to items that do not have a stored inflected form available.

The major contribution of this thesis is to test the rule component of the Words-and-Rules theory on the basis of Dutch pluralisation, including newly collected acquisition data. Dutch is a language that seemingly has two plural affixes acting as defaults, -s and –en. Investigating acquisition is motivated by the claim that the theory is universal, which suggests that children acquiring Dutch should look for a single default, despite the input they receive. Experimentally obtained data reported on in this thesis (including data from children between just under three and six years of age and adult controls) force a reconsideration of the rule component of the theory. Speakers of Dutch, adults and first language learners, have only one true default, but the rival affix is still regular. This finding leads to a modification of the theory towards a constraint-based model of Words-and-Constraints, in which crucially the possibility exists to differentiate defaults from regulars.

The Acquisition of the Dutch Plural is of interest to researchers in the fields of phonology, psycholinguistics, language acquisition and morphology.