has用于第三人称单数，have用于第一、第二人称以及第三人称复数。关于动词have(has)的用法。have用于第一人称（I，we)，第二人称(you)，及第三人称复数（they）；has用于第三人称单数（he，she，it)或单数名词。
have与to一起构成情态动词，表示“不得不”、“必须”，可用于各种时态。
I have to look after her at home.
have做助动词与动词的过去分词一起构成现在完成时和过去完成时。
Great changes have taken place the last two years.
They said that the Arab had stolen their camel.
have用于“情态动词＋have＋过去分词”的结构，有推测、假设之意。
1.must＋have＋过去分词，表示对过去时间发生的动作或存在的情况的推测，一般用于肯定句。
Her father thought that she must have met a fairy.
You must have left your bag in the theatre.
2.can(could)＋have＋过去分词，表示对过去发生事情的“不肯定”，常用于否定句和疑问句。
He can't have been to your home, he doesn't know your address.
3.should＋have＋过去分词，表示“某事本该早做而实际未做”，用于肯定句。
You should have been here five minutes ago.
have用于某些成语，表示固定的意思。
1.have a word(a few words)with sb.，表示和某人说一（几）句话。
Where's Peter? I want to have a word with him.
2.had better＋不带to的动词不定式，表示“…最好…”。
I'd better go and look for him now.
3.have nothing(something)to do with，表示“和…无（有）”关系。
Most of questions had nothing to do with Edison's lessons.
