A theory in science is a logical explanation or description of an occurrence or observation, or a verified hypothesis or proven model of the manner of interaction of natural phenomena, which can be used to predict future occurrences or observations of the same kind, and which is capable of being falsified through empirical observation.
The Oxford English Dictionary defines "theory" as:
- A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles, or causes of something known or observed.
An example of a theory is thus: It is a fact that an apple or indeed any object has been observed to fall towards the center of the planet when dropped; the theory of gravity is the theory which explains why this happens.
This definition differs from the layman's definition, which is synonymous with the terms 'conjecture,' 'opinion,' or 'guess' while for scientists theory and fact do not necessarily stand in opposition. It is this difference in definition which often causes many to misuse the term 'theory' in scientific contexts and misunderstand what a theory is and isn't. This misconception is a common theme in the criticisms of quite a few theories, including that of evolution.
Theory and Fact
Oftentimes, a theory is the result of a hypothesis or even a conjecture which was tested through experiment many times and found to hold up well. If the results of an experiment contradict the hypothesis or theory, the hypothesis or theory is either modified to fit the newly discovered information, or discarded and a new one is formed if it cannot be modified. It is not a guess that natural selection drives evolution; it is in fact supported by plenty of evidence found through investigation, study, and experimentation. Finally, a distinction should also be made between fact and conjecture: It is not a guess that evolution, as a process, happens; it too is supported by plenty of evidence, so much that one simply cannot reasonably argue that evolution doesn't happen, and would be stupid to try unless he had new, groundbreaking evidence which truly called it into question.
The Theory of Evolution as a fact
A distinction should be made between theory and fact: It has been observed that life on Earth evolves ÃÂ¢ÃÂÃÂ that is, the allele frequencies of genes in a given genetic population do change from generation to generation, and these changes do accrue to eventually result in new species. This is not in question by any scientist. This genetic phenomenon is recognized as the law of evolution, which is the subject of this article. The theory of evolution is a well-tested explanation of what drives the evolutionary process; the theory with the most evidence supporting it by far is that of natural selection, and the article on natural selection is where the theory of evolution would be covered.
The theory of evolution is not evolution itself, in the same manner that the theory of gravitation which explains, for example, why the Earth orbits around the Sun is not itself the Earth orbiting around the Sun. And just as disproving the theory of gravity would not prove the Earth doesn't orbit around the sun (only that gravity isn't the cause), disproving the theory of natural selection would not prove evolution doesn't happen (only that natural selection doesn't drive it). A distinction should also be made between theory and conjecture: A conjecture is a plain guess. A theory is a well-tested model which explains observed phenomena and with which one can make predictions about future observatio.
Just remember that a theory is just a theory. Which means you can dismiss it at a whim.