Engineering
Engineering is the creative application of science, mathematical methods, and empirical evidence to the innovation, design, construction, operation and maintenance of structures, machines, materials, devices, systems, processes, and organizations. The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, and types of application. See glossary of engineering.
Theory
A theory is a contemplative and rational type of abstract or generalizing thinking, or the results of such thinking. Depending on the context, the results might, for example, include generalized explanations of how nature works. The word has its roots in ancient Greek, but in modern use it has taken on several related meanings.
Theory
During the period that began with classical Greece and ended with late pagan antiquity, philosophy was more than merely a theoretical discipline. Even when Aristotle identified philosophy with "theory," his purpose is to argue ... that a life of theoretical activity, the life of philosophy, was the best life that human beings could lead.
Alexander Nehamas, The Art of Living (1998)