In this paper we discuss the characteristics that are habitually assigned to collocations: binarism, belonging to the norm and arbitrariness and show that these properties do not in fact define them. 1) The binary relationship between the base and the collocate is contradicted by the possibility of combining the same collocate with a number of bases. 2) The assumption that collocations belong to the norm is refuted by the existence of semantic paradigms formed by bases which combine with the same lexical unit: the collocate. 3) The very existence of semantic paradigms is not an arbitrary phenomenon, but rather, a consequence of the meaning of the units that constitute them, the bases, one of whose semantic features forms part of the meaning of the collocate. Thus, we can conclude that collocations are radial syntagmatic structures in which one semantic feature of the collocate determines its combination with a lexical class of units, bases, which share the same feature.