This article classifies prepositions and complex prepositional phrases in terms of their ability to license a null object, or, in other words, in terms of their ability to occur as orphan prepositions (Zribi-Hertz 1984). I adopt an extended PP projection and draw on Roberge (2012), who correlates the licencing of null objects in the verbal domain to those in the prepositional domain, in order to formalize and sharpen widely accepted intuitions that prepositional null objects are licensed by prepositions with some degree of rich lexical content. A tripartite distinction emerges which involves functional prepositions of the category p, lexical prepositions of the category P, and prepositions built around a nominal element. The account unifies these three types of preposition and motivates syntactically complex representations for forms that, superficially, do not appear to be complex.