Brown and Levinson's politeness theory

The politeness theory was first developed by acclaimed linguists Penelope Brown and Stephen Levinson. It states that in every conversation we adhere to certain language rules depending on the other participant's 'face', in order to assure that everyone feels affirmed in any social interaction. 'Face' is the public self-image that every person aims to protect, and it is vulnerable to 'face-threatening acts'.

Face comes in two forms: positive and negative. By using politeness strategies we can influence a person more effectively by appealing to their different faces.

Positive face - The need to feel appreciated and cared for.
Negative face - The need to not have one's freedom of choice infringed on.

The four different types of politeness:

Positive politeness aims to minimize the threat to a person's positive face, so it will make the participant feel good about himself and his wants.
E.g, "Excuse me, mate - pass the salt?"
The colloquial noun 'mate' causes the other participant to feel wanted and appreciated, thus appealing to their positive face.

Negative politeness aims to minimize the threat to a person's negative face, so it will try to minimize the imposition on the hearer.
E.g, "Could you pass me the salt?"
The epistemic modal auxiliary verb 'could' indicates to the hearer that passing the salt is not a demand - it is a possibility and they have the free choice whether to do so or not.

Bald-on record politeness - This type of politeness doesn't really try to minimize the threat to a hearer's face; it is very direct and most often only used when the speaker has a close relationship with the hearer. E.g, "pass me the salt."

Off-record (indirect) politeness - This type of politeness uses indirect language to hint at its goal, rather than saying it outright. E.g, "god, I'd REALLY love some salt right now."