A theory is a systematic and rational form of abstract thinking that explains a phenomenon or a set of related phenomena. It involves logical reasoning, often supported by observation, experimentation, and research, to provide a coherent explanation of facts or events

. In science, a theory is a well-substantiated explanation of some aspect of the natural world, based on a body of evidence repeatedly confirmed through observation and experiment. Scientific theories are comprehensive, testable, and capable of making falsifiable predictions, distinguishing them from hypotheses or unproven ideas. Examples include the theory of evolution, atomic theory, and the theory of relativity

. More broadly, a theory can be a set of conceptual tools that help describe, explain, and make claims about the world. It provides accurate descriptions, systematic explanations of causal mechanisms, and knowledge claims that can be tested either abstractly or empirically

. Outside of science, the term "theory" can also refer to ideas or principles intended to explain facts or events, though these may not be as rigorously tested as scientific theories. In everyday language, "theory" is often contrasted with "practice," meaning what is expected or hypothesized versus what is actually done or observed

. In summary, a theory is:

• A structured set of ideas explaining phenomena.
• Supported by evidence and logical reasoning.
• In science, a well-tested and reliable explanation.
• A tool for making predictions and guiding further inquiry