there are many themes but the title itself could be one. it portrays people who use their sense and others who don't, similar to pride and prejudice. you can compare Elinor and Marianne, sisters but Elinor uses her sense and reality to base life, Marianne is the opposite. Marianne ends up misjudging Willoughby's interest and thought he'll marry her but he did not. there are other elements as well though, such as themes of marriage, wealth, etc..