We often try to introduce students, especially in higher Elementary and Pre-Intermediate levels, to ‘Could you …’ type polite requests but I’ve found that textbooks do not always explain quite adequately exactly WHY one form is more polite than another. This is a simple little activity that might make it a little clearer and students have found helpful.
First, think about household requests (field), like hang the washing out, do the washing up, etc. and write each request on a piece of small paper. Next, write on the whiteboard the following:
1. Open the door please.
2. Will you open the door please?
3. Can you open the door please?
4. Could you open the door please?
5. Would you mind opening the door please?
6. You wouldn’t mind opening the door would you please?
The activity is then very simple. A student picks up a piece of paper with an activity written (‘turn on the heater’), rolls a dice (‘5’) and uses the corresponding form from the list (Would you turn on the heater please?).
Either before or after the activity we can look at just why some forms appear more polite than others. Students often assume that one form is inherently more polite than another but this is not really the case. I think the answer is in different forms of grammatical metaphor. In terms of the discourse semantics of exchange all six of the requests above are exactly the same – a demand for service. In only first one, however, does the lexico-grammar match the semantics with an imperative clause. From there we go through a series of changes through grammatical metaphor that puts distance between the discourse function and lexico-grammatical form.
From 1. to 2. we change from imperative to interrogative clause. Then, in 3., we change the element of modality and then from 3. to 4. there is a further shift from present to past tense. This use of the past tense for politeness, by putting (metaphorical) distance between the speaker and the lexico-grammar, is often new to most students but can be an important part of politeness in English (compare Do you want…? with Did you want…? for example). Then, in 5., there is an example of nominalisation (open → opening) and a shift from a material Process to a mental one (mind). Finally, there is a change from an interrogative clause to a declarative clause + tag.