A hypothesis is a proposed explanation for some event or problem.
Cardinal Bellarmine gave a well known example of the older sense of the word in his warning to Galileo in the early 17th century: that he must not treat the motion of the Earth as a reality, but merely as a hypothesis.
Today, a hypothesis refers to an idea that needs to be tested. A hypothesis needs more work by the researcher in order to check it. A tested hypothesis that works, may become part of a theory or become a theory itself. The testing should be an attempt to prove the hypothesis is wrong. That is, there should be a way to falsify the hypothesis, at least in principle.
People often call a hypothesis an "educated guess".
- "When it is not clear under which law of nature an effect or class of effect belongs, we try to fill this gap by means of a guess. Such guesses have been given the name conjectures or hypotheses". Hans Christian Ørsted (1811).
- "In general we look for a new law by the following process. First we guess it. ..."
Experimenters may test and reject several hypotheses before solving the problem.
A 'working hypothesis' is a hypothesis that is provisionally accepted as a basis for further research. The hope is that a theory will be produced, even if the hypothesis ultimately fails.
- Working hypothesis: a hypothesis suggested or supported in some measure. Consequences may be deduced which can be tested by experiment and special observations. It is proposed to do such investigation, with the hope that, even should the hypothesis thus be overthrown, such research may lead to a tenable theory.
In recent years, philosophers of science have tried to integrate the various approaches to evaluating hypotheses, and the scientific method in general, to form a more complete system. Notably, Imre Lakatos and Paul Feyerabend, Karl Popper's colleague and student, respectively, have produced novel attempts at such a synthesis. Some people take to using the zetetic method to attempt this.