Science is the explanation of phenomena by natural processes. Scientific theories must be testable and their conclusions are falsifiable and subject to change.

Fact
In science, an observation that has been repeatedly confirmed and for all practical purposes is accepted as "true". Truth in science, however, is never final, and what is accepted as a fact today may be modified or even discarded tomorrow.

Hypothesis
A tentative statement about the natural world leading to deductions that can be tested. IF the deductions are verified, it becomes more probable that the hypothesis is correct. If the deductions are incorrect, the original hypothesis can be abandoned or modified. Hypotheses can be used to build more complex inferences and explanations.

Law
A descriptive generalization about how some aspect of the natural world behaves under stated circumstances.

Theory
In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

Important differences between the scientific use of the words theory and fact and common use of these words. In science theories do not turn into facts through the accumulation of evidence. Rather, theories are the end points of science. They are understandings that develop from extensive observation, experimentation, and creative reflection. They incorporate a large body of scientific facts, laws, tested hypotheses, and logical inferences.