them from prepositions, but many do not. One simple test that is often telling is to modify the phrase by right or just. In Standard English, adverb phrases do not accept such modification (e.g., it ran right up the tree [PP]; *it ran right vertically [AdvP].) Also, PPs commonly function as complements in a be VP (e.g., it's in the car), while adverbs cannot normally do so. Prepositions vs complementizers "Complementizer" is a term which has its origins in generative grammar. It refers to a restricted subset of what are classified as subordinating conjunctions in traditional grammar. There are only a very few complementizers: that, whether, and if are the main examples. Traditional grammar includes words like because, while, and unless in the class of subordinating conjunctions. But since at least Jespersen (see ) most modern grammarians distinguish these two categories based on whether they add meaning to the sentence or are purely functional. The distinction can be shown with if, since there is a complementizer if and a preposition if. The preposition introduces a conditional meaning (e.g., if it works, that's great). Complementizers, though, have no meaning. They just mark a clause as subordinate; there is no difference in meaning between I know that you were there and I know you were there. Similarly, in She asked if we were there the complementizer if merely marks the following clause as a closed interrogative content clause, without adding any conditional meaning. The syntax of prepositions and PPs Internal structure PPs are usually quite simple in their internal structure. The following syntax tree shows a PP with an adverb phrase as modifier and a head PP. The head PP has a head preposition in and an object NP the rain. When the preposition governs an argument of a larger phrase, such as a noun phrase, the object of the preposition is sometimes called a prepositional or oblique argument. For example, convert the energy of ocean waves into electricity becomes the conversion [of the energy of ocean waves] into electricity, where the underlined NP – which is the object in the PP headed by of – is the oblique argument of conversion. Postpositions A very small number of prepositions (see ) may occur after their object, for example, notwithstanding, which can appear either before the object (e.g., notwithstanding the fact) or after (e.g., the contrary notwithstanding). Complements of prepositions Traditional grammars of