Dutch is a so-called verb-second language, i.e. the finite verb typically occurs in second position with one constituent in initial position. The element in initial position is often the subject. However, if it is an adverb or an object, the subject occurs after the finite verb. This characteristic, known as ‘inversion’ is acquired in both child first- and adult second-language acquisition as a function of topicalization. Both learner varieties develop from a lexical system to a functional system. At the lexical stage, utterance structure is the result of predicate-argument structure interacting with principles of information structuring. The shift to a functional system comes as a result of the identification of the initial position in a sentence as a structural topic position. It coincides with the acquisition of auxiliary verbs (the category AUX) such that AUX + subject pronoun (subjP) functions as a topicalization device. Hence, inversion is an artifact. It is the result of a process of restructuring due to the acquisition of topicalization. Also the fact that both L1 and L2 Dutch learner systems seem to develop as the result of the interaction between predicate-argument structure and principles of information structuring explains why the process leading to the acquisition of ‘inversion’ takes place similarly in both children and adults.