The short answer is no. You cannot copyright someone else’s written work, and simply adding sources does not protect you from copyright infringement. While I am an AI and not a lawyer, I can break down the basic facts of copyright law to explain exactly why this doesn't work, and what happens to that "50%" scenario you mentioned. Citing Sources vs. Copyright Infringement People often confuse plagiarism with copyright infringement, but they are two completely different things: Plagiarism is an ethical issue: It means passing someone else's work off as your own. You fix plagiarism by citing your sources. Copyright is a legal issue: It is the exclusive legal right to reproduce, distribute, and sell a piece of work. Citing a source does not give you the legal right to copy someone's work. If you copy someone else's writing without their explicit permission (a license), you are violating their copyright, regardless of whether you give them credit. The "50%" Scenario: What Actually Happens? If you write a book and 50% of the text is taken directly from someone else's copyrighted work, here is how the law views it: 1. You only own what you created. You would technically own the copyright to the 50% of the book that consists of your original words and thoughts. You can never claim copyright over the 50% that the other person wrote. 2. It is an "Unauthorized Derivative Work." By mixing your original work heavily with someone else's copyrighted work, you have created a "derivative work." Only the original copyright holder has the right to authorize derivative works. Because you used a massive chunk (50%) of their property without permission, your book is legally compromised. 3. You cannot legally publish or sell it. Even though you own half the words, you cannot publish, sell, or distribute the book because it contains stolen property. The original author could issue a takedown notice or sue you for damages. What About "Fair Use"? There is a legal doctrine called Fair Use, which allows you to quote small portions of copyrighted work without permission for specific purposes, such as: Criticism or review News reporting Teaching or academic research However, Fair Use is highly restrictive. It usually only covers brief excerpts (like a sentence or a short paragraph). Using 50% of someone else's work goes far beyond any accepted definition of Fair Use. It would be seen as a market substitute for the original work. The Public Domain Exception The only exception to this is if the work you are using is in the Public Domain (meaning the copyright has expired, like works by Shakespeare or Edgar Allan Poe). If you use 50% public domain text and 50% your own original writing: You can legally publish and sell the book.