The usual conception of valency found in the literature links all cases of semantic role assignment to the properties of verbs. It is commonly held that a verb determines the number and form of its complements, and assigns to each of them a semantic role: this is usually taken to be a fair summary of the process, and underlies the elaboration of valency dictionaries. The idea is that, once the valency of a verb is stated, the syntactic form and semantic roles of its complements are accounted for; and that they are determined on the basis of the valential properties of the verb. Reports on valency usually start from the idea that valency is “the number of actants a verb is susceptible to govern,” and express at most some hints at the existence of further factors. In this chapter decisive evidence is presented to show that the system is vastly more complex than traditionally believed, and includes several kinds of factors, not all of them dependent on the verb, and not all linguistic stricto sensu. Besides, not only semantic roles are involved: there is an important process assigning elaborate thematic relations, directly taken from the evoked schema, to complements in the sentence.