The predicative noun is used with the indefinite article if the speaker states that the object denoted by the noun belongs to a certain class. If a predicative noun is modified by a particularizing attribute, the definite article is used. He is the student you wanted to speak to. If a predicative noun denotes a post that can be occupied by one person at a time, either no article or the definite article is used. Mr. Henderson is manager, not under-manager any longer. (Lindsay) Montanelli was director of the theological seminary at Pisa.  Comrade N. is the dean of our [...]