A theory, to scientists, means something rather different from its popular use, which suggests something speculative or untested. A scientific theory is a cohesive body of knowledge, an explanation that is consistent among a range of cases and can allow you to predict what might happen in unknown situations.

The time is always ripe for the re-interpretation of theories in the light of new vision and of new facts. This is the very province of science.

A scientific theory is a concise and coherent set of concepts, claims, and laws (frequently expressed mathematically) that can be used to precisely and accurately explain and predict natural phenomena.
A theory should include a mechanism that explains how its concepts, claims, and laws arise from lower-level theories.

A theory, is a body of knowledge, that is supportive of, and explanative of facts. Scientific laws are included within a theory, facts are included within a theory, that's why you have the theory of evolution, the theory of gravity, the theory of relativity. There is no concept in creationism, which meets any of the qualifications of a scientific theory, none. You have no facts, you have no laws, you have no evidence, you have no explanative power. All you have, is whatever science can't explain, you pretend you can.

The theory of universal gravitation is not cast-iron. No theory is, and there is always room for improvement. Isn't that so? Science is constructed out of approximations that gradually approach the truth. . . Well, that means all theories are subject to constant testing and modification, doesn't it? And if it eventually turns out that they're not quite close enough to the truth, they need to be replaced by something that's closer. Right?

Scientific theories are distinguished from myths... in being criticizable, and... open to modifications... They can be neither verified nor probabilified.

[we see that] science is eminently perfectible, and that each theory has constantly to give way to a fresh one.

Scientific theories can always be improved and are improved. That is one of the glories of science. It is the authoritarian view of the Universe that is frozen in stone and cannot be changed, so that once it is wrong, it is wrong forever.

The extensive literature addressed to the definition or characterization of science is filled with inconsistent points of view and demonstrates that an adequate definition is not easy to attain. Part of the difficulty arises from the fact that the meaning of science is not fixed, but is dynamic. As science has evolved, so has its meaning. It takes on a new meaning and significance with successive ages.

When the theory performs well you also think, “Are there parallel results in naturally occurring field data?” You look for coherence across different data sets because theories are not specific to particular data sources. Such extensions are important because theories often make specific assumptions about information and institutions which can be controlled in the laboratory, but which may not accurately represent field data generating situations. Testing theories on the domain of their assumptions is sterile unless it is part of a research program concerned with extending the domain of applications of theory to field environments

At any one time there is a natural tendency among physicists to believe that we already know the essential ingredients of a comprehensive theory. But each time a new frontier of observation is broached we inevitably discover new phenomena which force us to modify substantially our previous conceptions. I believe this process to be unending, that the delights and challenges of unexpected discovery will continue always.

Scientific theories need reconstruction every now and then. If they didn't need reconstruction they would be facts, not theories.

Under my definition, a scientific theory is a proposed explanation which focuses or points to physical, observable data and logical inferences. There are many things throughout the history of science which we now think to be incorrect which nonetheless would fit that — which would fit that definition. Yes, astrology is in fact one.

Science is not a monolithic body of doctrine. Science is a culture, constantly growing and changing. The science of today has broken out of the molds of classical nineteenth-century science, just as the paintings of Pablo Picasso and Jackson Pollock broke out of the molds of nineteenth century art. Science has as many competing styles as painting or poetry. The diversity of science also finds a parallel in the diversity of religion.