3.1　CATEGORIESOF INVITATIONS

Based on their different forms，invitations fall into two categories：invitation letters and invitation cards.An invitation letter resembles a business letter.Its wording is usually conversational，as though the writer were extending the invitation orally.Invitation cards，by comparison，are more formal than invitation letters in that they are fixed in structure pattern.Besides，compared with an invitation letter，there are usually fewer words in an invitation card，which provides only important information of the gathering and leaves out the details.(https://www.daowen.com)

With the simplification of social contact codes，invitation letters are more widely used.However，on some formal occasions，it is still necessary to send invitation cards.