Since the introduction of the X-bar principles it is commonly assumed that prepositions are heads of PPs, in the same way as nouns and pronouns are heads of NPs. However, while this is well motivated for a large majority of the pronouns and the prepositions in many languages, there are also exceptions. More specifically, Van Eynde (1999) argues that the reduced or minor pronouns of Dutch---as opposed to their full or tonic counterparts---cannot head an NP, and the purpose of this paper is to demonstrate that there are also prepositions which cannot head a PP. The first section introduces the distinction between major and minor categories. The second shows how it can be applied to the prepositions and presents a way of treating minor prepositions in HPSG. The third singles out the Dutch te (to) as a plausible candidate for a minor preposition treatment, and the fourth provides criteria for the identification of other minor prepositions. The concluding section points out the wider significance of these findings.