Omniglot - Writing systems of Human Beings

"In A History of Writing, Steven Roger Fischer argues that no one definition of writing can cover all the writing systems that exist and have ever existed. Instead he states that a 'complete writing' system should fullfill all the following criteria:
Complete writing must have as its purpose communication;

Complete writing must consist of artificial graphic marks on a durable or electronic surface;

Complete writing must use marks that relate conventionally to articulate speech (the systematic arrangement of significant vocal sounds) or electronic programing in such a way that communication is achieved."

via memepool