Memo is short for “memorandum”， which means a short official notethat is sent by one person to another within the same company ororganization. Memos， including memos sent through email， are simplemeans of communication within an organization. Compared with businessletters， they are simple because they usually omit the formality of theexpensive letterhead， inside address， salutation， complimentary close， andsignature block， which are commonly used in business letter. They areefficient because their simple and direct composition conveys quickly whatthe write wants to say to the reader.
　　Memos can be typed according to their circulation way. Generallyspeaking， there are four types of memos： （1） sent to upper management：acting as a report and goes to upper management. （2） sent to divisionsaffiliated： carrying instructions from upper management. （3） sent to all ofthe staff： working as a notice or bulletin. （4） sent to colleagues in oroutside one's own department： exchanging information.
　　A memo serves a very useful purpose， it is an effective and efficientcommunication tool. Generally speaking， companies use memos toannounce policies， spread information， delegate responsibilities， instructemployees， and report the result of an investigation. Companies also relyon memos to keep employees informed about company goals， to motivateemployees to achieve the goals， and to build employee morals.2. The introduction of cooperative principle and politenessprinciple