The inaccurate use of stress or intonation can cause problems. Listen to the following request by a non-native speaker:

Do you mind if I OPEN the window?

Notice how the sentence stress is on the əʊ of /ˈəʊ p ə n /(open). As it was a first request, one might have expected the first syllable of window to have been the most prominent, rather than the first syllable of open. The sentence could be interpreted as a second request (the first request perhaps not having been heard), which may seem rude to the listener.

Listen to another example:

The unexpected fall of the intonation makes the question difficult to understand. (One would expect the voice to fall on the first syllable of LONdon).
Intonation and stress can also indicate the function of an utterance. The function of an utterance is what it is being used for. For example, the following sentence has the function of a ‘request’:

Can you help me, please?

But consider this sentence:

As a first ‘suggestion’ or ‘invitation’, the first syllable of party is stressed, as indicated with capitals, and hear the voice go down at the end, as shown by the arrow. Now consider this variation:

This question doesn’t seem to be a simple invitation. It suggests instead that someone has refused the invitation and that the speaker is upset and needs to know what has happened. Using this stress and intonation for a straightforward invitation rather than speaking as in the first example, makes a misunderstanding possible.