The phrase "deaf to reason" means to be unwilling or unable to listen to rational arguments. Some synonyms for this phrase include "unresponsive," "obstinate," "intractable," "stubborn," "unyielding," and "unreasonable." These words all describe individuals who are resistant to logical appeals and are often set in their own ways. Someone who is deaf to reason may also be described as "close-minded" or "prejudiced," as they are unwilling to consider alternative viewpoints or perspectives. It is important to recognize and understand these traits in individuals to effectively communicate and persuade them in important matters.