Copy Writing

How much can you copy from others, the golden rule is usually 10% of content, whether it be from a website or book. There is some grey area though is it 10% of the entire website or just of the page that is showing? This is where it is really important to followup and make sure that permission is granted by the publishers of these sites. All material that is copied or used from any source has to be referenced back to the author otherwise it is plagiarism, which we all know is illegal.