We usually use certain syntactic structures with the functions listed beside them in the following table.

When an interrogative structure such as Did you…?, Are they…? or Can we…? is used with the function of a question, it is described as a direct speech act. For example, when we don’t know something and we ask someone to provide the information, we usually produce a direct speech act such as Can you ride a bicycle?.

Compare that utterance with Can you pass the salt?. In this second example, we are not really asking a question about someone’s ability. In fact, we don’t normally use this structure as a question at all. We normally use it to make a request. That is, we are using a syntactic structure associated with the function of a question, but in this case with the function of a request. This is an example of an indirect speech act. Whenever one of the structures in the set above is used to perform a function other than the one listed beside it on the same line, the result is an indirect speech act.

The utterance You left the door open has a declarative structure and, as a direct speech act, would be used to make a statement. However, if you say this to someone who has just come in (and it’s really cold outside), you would probably want that person to close the door. You are not using the imperative structure. You are using a declarative structure to make a request. It’s another example of an indirect speech act.

It is possible to have strange effects if one person fails to recognize another person’s indirect speech act. Consider the following scene. A visitor to a city, carrying his luggage, looking lost, stops a passer-by.

In this scene, the visitor uses a form normally associated with a question (Do you know…?), and the passer-by answers that question literally (I know… ). That is, the passer-by is acting as if the utterance was a direct speech act instead of an indirect speech act used as a request for directions.

The main reason we use indirect speech acts seems to be that actions such as requests, presented in an indirect way (Could you open that door for me?), are generally considered to be more gentle or more polite in our society than direct speech acts (Open that door for me!). Exactly why they are considered to be more polite is based on some complex social assumptions.