A hypothesis (plural hypotheses) is an explanation proposed for a phenomena. The scientific method demands that a hypothesis be testable in order for it to be considered a scientific hypothesis. Scientists often develop scientific hypotheses on earlier data that cannot be explained satisfactorily by the established scientific theories. Despite the fact that the terms “hypothesis” and “theory” are sometimes used interchangeably, a scientific hypothesis is not the same as a scientific theory. A working hypothesis is a hypothesis that has been tentatively accepted and is being offered for further investigation, in a process that begins with an informed guess or notion.