In this article, the definitions of the attribute, classified within the sphere of Spanish linguistics, are grouped together in three sections: those based on the idea of quality; those based on the attribute, in opposition to the gramatical sense of the linking verb. These definitions are revised critically and, as a result of the problems arising from them, we put forward a definition of the attribute based on our theories. In the second part of the article, the possibility of using proforms of the attribute as criteria for classifying semantically the predicative nucleus of attributive sentences is considered. The third part deals with problems deriving from the interpretation of the infinitive, the participle and the gerund as attributes of one element of the sentence. Finally, we point out the inadequacies of certain classifications of the attribute and conclude by stressing the need for empirical research into the type of sentences which include this syntagmatic function.