The phrase "talk like a book" originated from the idea of someone speaking in a manner that resembles the formal and precise language found in written books. It is used to describe someone who speaks in a formal or intellectual manner. It suggests that the person's speech is characterized by a careful choice of words, clarity of expression, and adherence to grammatical rules. This idiom is often used to comment on someone's speaking style, particularly when it comes across as overly formal or lacking in natural conversational tone. It can be used in both positive and negative contexts, depending on the intention and perception of the speaker.