University professors teaching pre-service teachers base much of their philosophies on theories. Students often ask "Why do we have theories?" "What is the purpose of theories?" "If we like a theory, do we have to use all of the theory?" The most frequent controversial issue is how to use a particular theory in a practical way. In the quest for these answers, students begin to realize that there are no completely right theories. This realization is the exciting part about studying and analyzing theories. Students learn that a "theory" is an orderly, integrated set of statements that describes and predicts behavior. Theories are influenced directly by cultural values and belief systems of their times. Theories are vital: They guide and give meaning to what we see. When a researcher investigates and collects information through observation, the investigator needs a clear idea of what information is important to collect. Thus, valid theories are validated by research and are a sound basis for practical action. In this article, common theories are analyzed including theorists, John Locke, Jean-Jacque Rousseau, Piaget, and Vygotsky. The article concludes with several important points for discussion: (1) Many theories are extreme in nature; (2) Educators use a combination of theories in their classrooms; (3) Theories get issues and concerns on the table for discussion; (4) Theories serve an important purpose; and (5) Research, resulting in theories, should not govern everything we do in life; there is a time that common sense and gut instinct should override theories. The open-minded individual considers them all!