A direct illocution is an illocutionary act in which only the illocutionary force and propositional content literally expressed by the lexical items and syntactic form of the utterance are communicated.
Searle, John, and Daniel Vanderveken. 1985.Foundations of illocutionary logic. Cambridge, England: Cambridge University.
Searle, John. 1979.Expression and meaning: Studies in the theory of speech acts. Cambridge, England: Cambridge University.
Levinson, Stephen C. 1983.Pragmatics. Cambridge, England: Cambridge University.
Leech, Geoffrey. 1983.Principles of pragmatics. London: Longman.