Computer
A computer is a device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Modern computers have the ability to follow generalized sets of operations, called programs. These programs enable computers to perform an extremely wide range of tasks.
Computer Science
Computer science is the study of the theory, experimentation, and engineering that form the basis for the design and use of computers. It is the scientific and practical approach to computation and its applications and the systematic study of the feasibility, structure, expression, and mechanization of the methodical procedures (or algorithms) that underlie the acquisition, representation, processing, storage, communication of, and access to, information. An alternate, more succinct definition of computer science is the study of automating algorithmic processes that scale. A computer scientist specializes in the theory of computation and the design of computational systems. See glossary of computer science.
Mathematics
Mathematics (from Greek μάθημα máthēma, "knowledge, study, learning") is the study of such topics as quantity, structure, space, and change. It has no generally accepted definition.
Science
Science (from Latin scientia, meaning "knowledge") is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
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)
Computer Science
Any problem in computer science can be solved with another level of indirection.
David Wheeler (Attributed in: Butler Lampson. Principles for Computer System Design. Turing Award Lecture. February 17, 1993.) Wheeler is said to have added the appendage "Except for the problem of too many layers of indirection."
Theory
If you refuse to take account of theory, then you have forgotten that practice is often an offspring of theory.
Fausto Cercignani in: Brian Morris, Simply Transcribed. Quotations from Writings by Fausto Cercignani, 2014, quote 54.