A statement that explains a set of facts and can be tested to determine if it is false or inaccurate.
Usage The words hypothesis, law, and theory refer to different kinds of statements that scientists make about natural phenomena. A hypothesis is a statement that attempts to explain a set of facts. It forms the basis for an experiment that is designed to test whether it is true. Suppose your friend Smedley's room is a mess; your hypothesis might be that Smedley makes the room messy. You could test this hypothesis with an experiment: tidy up the room and see if it becomes messy again after Smedley returns. A scientific law is a statement that is believed to be true all the time for a set of conditions. If Smedley's room is always a mess when he is in it, you might propose a "Smedley's Mess Law" stating that whenever Smedley is in his room, he will always
make it messy. Laws have the power to predict what will happen under the conditions they apply to. Thus, "Smedley's Mess Law" predicts that Smedley's room will be messy anytime Smedley is in it. A theory is a set of principles or statements devised to explain a whole group of observations or phenomena. A theory thus tries to account for a wider variety of events than a law does. Broad acceptance of a theory comes when it has been repeatedly tested experimentally on new data and makes accurate predictions about them. If people noticed that it became messy everywhere Smedley went, it might lead to the theory that Smedley brings messiness wherever he goes. This theory could be tested by bringing Smedley somewhere he's never been.
1. a principle or proposition that is assumed for the sake of argument or that is taken for granted to proceed to the proof of the point in question.