Not just semantics. A more detailed explanation is required. Scientific theories are explanations of natural phenomena developed from logical hypotheses and testable observations and experiments. Science uses the word 'fact' when referring to something that has been tested or observed so many times that there is every reason to accept the evidence and testing as offering every compelling reason to accept the data as repeatable and accurate. The occurrence of gravity as well as biological evolution in this sense are facts. Scientists no longer question whether gravity or biological evolution are quantifiable because the evidence supporting the theories are so strong. A law as described in science is a generalization that describes a natural phenomena. Note that science deals with natural phenomena as supernaturalism is not a science matter. A theory is an explanation of a natural phenomenon. For example, the law of gravity describes the motion of objects under certain circumstances when affected by other objects; the theory of gravity explains why these events occur. Laws, like facts and theories, can change with new data.Semantics. In any case, belief does not require proof. But I think you already knew that.