In Dutch, the distinction between composed and derived verbs is traditionally based on the separability of the verb and the positional and phonological characteristics this implies: separable verbs are considered to be composed verbs or to illustrate an intermediate category between composed verbs and syntactic groups, while the class of derived verbs only contains inseparable verbs. However, if we situate composition and derivation on a cline of grammaticalization and if we study the behaviour of Dutch preverbs according to morpho-syntactic and semantic grammaticalization parameters, we notice that the traditional distinction based on the criterion of separability does not coincide with the results of the application of our grammaticalization parameters: less grammaticalized preverbs, which behave as adpositions or adverbs and which are supposed to introduce composed verbs, can be inseparable, while more grammaticalized preverbs, acting as true prefixes, can be separable. In our contribution, we will examine this paradox more profoundly.