When it comes to evaluating a situation, people often need to compare and contrast different perspectives. If two people are "in the same book," it means they are on the same page or have similar opinions about a subject. However, there are many other phrases and expressions that can be used to convey the same meaning. Some of these synonyms include: aligned, of one mind, in agreement, in harmony, of the same mindset, agreed, concordant, and of the same accord. Using these synonyms can help people communicate more effectively and avoid using the same phrase or expression too often.