Pass the salt.Here the word "please" softens or mitigates the request, making it more polite. This is not possible in a unix-like commands notation:
 Please pass the salt.
Requests are a kind of speech act. A speech act is a sentence (or fragment) that actually accomplishes something just by its being given. Some examples of speech act that are more obvious are christening ("I hereby name this ship the Queen Mary!") and marrying ("I hereby pronounce you man and wife!"). The theory of speech acts began with Austin and was further developed by Searle and others.
Each class of speech act has certain preconditions, also called felicity conditions, that must be met before it is well formed. Preconditions for requests include: (1) the speaker must genuinely wish the request to be carried out, and (2) the addressee must be capable of carrying it out. There is a general mitigation device for requests that causes what looks like a query about a precondition for a request to be interpreted as the request. For example,
 Can you pass the salt?is literally a request for information, but since that information concerns the precondition of the request , it is interpreted as . Similarly,
 I would like some salt.literally reports a state of mind, but since that state of mind is a precondition for the speech act , it is interpreted as . Speech acts that are accomplished in this way are called indirect speech acts. Thus we have shown that mitigating a speech act by indirection is one way to accomplish politeness.
In a context where politeness is not expected, for example, a king at dinner, sentences like  and  might well be interpreted literally, rather than as mitigated (i.e., nuanced) requests.