来自English Grammar Today
We use formal language in situations that are serious or that involve people we don’t know well. Informal language is more commonly used in situations that are more relaxed and involve people we know well.
Formal language is more common when we write; informal language is more common when we speak. However, there are times where writing can be very informal, for example, when writing postcards or letters to friends, emails or text messages. There are also examples where spoken English can be very formal, for example, in a speech or a lecture. Most uses of English are neutral; that is, they are neither formal nor informal.
Formal language and informal language are associated with particular choices of grammar and vocabulary.
Contractions, relative clauses without a relative pronoun and ellipsis are more common in informal language.
CompareShe has decided to accept the job.
formal
She’s decided to accept the job.
informal: She’s = contraction
CompareThe girl whom I met in Singapore was interested in working in Australia.
formal
The girl I met in Singapore was interested in working in Australia.
informal: relative clause without the relative pronoun whom
CompareWe went to Barcelona for the weekend. We have a lot of things to tell you.
Formal
Went to Barcelona for the weekend. Lots to tell you.
Informal: ellipsis (more likely to be written or texted than spoken)
More formal vocabulary commonly involves longer words or words with origins in Latin and Greek. More informal vocabulary commonly involves shorter words, or words with origins in Anglo-Saxon. Most dictionaries indicate very informal and/or formal words.
formal
informal
commence
start
terminate
end
endeavour
try
We often choose to use certain modal verbs to be more formal and polite:
Can I suggest you try this new model? (neutral)
May I suggest you try this new model? (more formal)
Might I suggest you try this new model? (very formal)
See also:
Contractions
Ellipsis
Speech into writing
Politeness