Theory is defined as a belief, policy, or procedure proposed or followed as the basis of action. Nursing theory is an organized framework of concepts and purposes designed to guide the practice of nursing.The first nursing theories appeared in the late 1800s when a strong emphasis was placed on nursing education.ursing Theory and the Nursing Process The nursing process is a scientific method used to ensure quality patient care that was first described in the 1950s and encompassed three steps.