An ELT Glossary : Illocutionary Act / Illocutionary force / Function
Definition and examples : Linguistics uses the terms "illocutionary act and "illocutionary force" with the same meaning as language teaching uses the term "function" (which has a different meaning in linguistics). The illocutionary force, or function, of an utterance is the action it is used to perform - eg the utterance "Why don't we go to the cinema?" carries the illocutionary force of making a suggestion; "Can you help me with this?" has the illocutionary force of making a request.
Further Information : Illocutionary force is dependent on context. In the dialogue ...
A : Why don't we get Sally a book for her birthday? / B : She hates reading.
B's utterance has the illocutionary force of rejecting a suggestion. However, the same utterance in a different context might have a completely different function - here, for example, it might constitute criticism :
A : She's never going to pass her exams. She hates reading and won't study.
Related Terms : Notion, Functional-Notional Syllabus