Illocutionary force is the status of an utterance as a question, promise, threat, etc. This term should not be confused with illocutionary act, which is a speech act, expressing the intention of the speaker.
The sentence Do you know what time it is? is uttered with the illocutionary force of a yes-no question, but uttering it is an illocutionary act of a request: it would be improper to answer with a simple 'yes'.
- Austin, J.L. 1962. How to Do Things with Words, Oxford University Press, Oxford.