Theories

A theory is a well-substantiated explanation of some aspect of the natural world. In science, theories integrate a body of observations, laws, and tested hypotheses into a coherent framework that explains how and why phenomena occur and enables reliable prediction. The term is often misused in everyday language to mean a guess, but a scientific theory is supported by substantial evidence and repeated testing, and it is open to revision.

Robust theories meet several criteria: they are testable and falsifiable, they coherently organize known facts, they have explanatory power that unifies diverse observations, and they generate testable predictions. They are refined through experiment, observation, replication, and peer review, and may be revised or replaced as new evidence emerges.

Examples include evolution by natural selection, germ theory of disease, plate tectonics, relativity, and quantum theory. These theories provide expansive accounts that apply across many phenomena and experimental contexts, though they may differ in scope and domain. Theories often coexist with models and assumptions, and scientists distinguish between well-supported theoretical frameworks and provisional or tentative ideas.

Theories are distinct from laws, which describe consistent relationships under specified conditions, often in mathematical terms, whereas theories seek to explain why those relationships hold. Theoretical knowledge evolves over time as evidence accumulates, and some domains maintain competing theories until consensus emerges.