ABSTRACT
Assertions are not facts. The identification of an assertion as science's subject matter may appear radical to some, as people frequently talk about science as dealing with facts. The conventional picture is that of a scientist searching for a pattern or some uniformity, one that he/she wants to report to peers and perhaps to a broader audience. What separates assertions and facts is uncertainty. Variation in the uncertainty level of assertions is endemic to both the substance and progress of science. While the fact/assertion distinction is the beginning point, an additional distinction warrants recognition. Definitions are also of critical importance to science, but they are not assertions. In the context of scientific activities an assertion is a scientific statement in the way of a claim, one set forth with the express or tacit understanding that it will be judged in light of data gathered to assess its predictive power relative to that of contenders.
