They express the relationship between objects and people, introduce complements. These small parts of speech are of great importance because they replace 'cases' in many other languages. They indicate various concepts such as: origin, destination, motion to place, finite and indefinite time, reason and purpose of action and also they give spatial and temporal information. For example, if I say, 'Marco viene DA Napoli,' I indicate the origin and that is where Marco started from. If I say, 'lavoro PER guadagnare,' I indicate the purpose of the action of working. If I say, 'il libro รจ TRA questi scaffali,' I indicate the location of the book