One of the goals of this research is to suggest some criteria that can organize some of the ideas we have about the prepositional phrase functions. We present fifteen different functions for prepositional phrases that can make an adjectivation possible in standard Portuguese. We try to show, also, how these fifteen ways can be synthesized, proposing a kind of fossilization of the preposition 'de' in Portuguese (somewhat equivalent to the preposition 'of' in standard English). We do not adopt one staight and inflexible theoretical position. Each problem that is found during the research is solved with the help of other theories and postulates, mainly related to functionalism.