You should already be familiar with common functions such as asking, telling, replying, thanking and suggesting.
Appropriacy noun appropriate/inappropriate adj.: Language which is suitable or correct in a particular situation. See register.
Colloquial: Language used in informal conversations or writing.
Declining, refusing an invitation: To refuse or decline an invitation, e.g. I’m sorry but I can't.
Enquiring: To ask for information, e.g. What time does the train leave?
Express: To show or make known a feeling or an opinion in words.
Expressing ability, e.g. I can swim.
Expressing intention, e.g. I'm planning to visit him next year.
Expressing necessity, e.g. He needs to get a new passport.
Expressing obligation, e.g. You must wear a seatbelt.
Expressing permission, e.g. Can I have a look at your book?
Expressing preference, e.g. I'd rather have coffee than tea.
Expressing probability, e.g. He should be in later.
Formal (language): see register.
Formality (level of): see register.
Function: The reason or purpose for communication, e.g. making a suggestion; giving advice.
Functional exponent: A phrase which is an example of a function and shows the purpose of the speaker, e.g. Let's... . This phrase is one way to make a suggestion. It is an example (or exponent) of the function of suggesting. See function.
Greeting: To welcome someone, often with words, e.g. Hello, how are you?
Inappropriate: see appropriacy.
Informal (language): see register.
Informality (level of): see register.
Instructing: To order or tell someone to do something, e.g. Please turn to page 12 and do exercise 1.
Negotiating: To have a discussion with someone to reach an agreement, e.g. If you help me now, I'll help you next week.
Neutral: A style of speaking or writing that is neither formal nor informal, but in-between. It is appropriate for most situations.
Predicting: To say what you think is likely to happen, e.g. I think the story will end happily.
Register: The formality or informality of the language used in a particular situation. Formal register or language is used in serious or important situations, e.g. in a job application. Informal register or language is used in relaxed or friendly situations, e.g. with family or friends.
Requesting, making a (polite) request: To ask someone politely to do something, e.g. Please could you open the window?
Speculating: To guess something, e.g. I think it might be an easy test.