Hypothesis

A hypothesis consists either of a suggested explanation for an observable phenomenon or of a reasoned proposal predicting a possible causal correlation among multiple phenomena.

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The scientific method requires that one can test a scientific hypothesis. Scientists generally base such hypotheses on previous observations or on extensions of scientific theories.

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A hypothesis is never to be stated as a question, but always as a statement with an explanation following it. It is not to be a question because it states what the experimenter thinks will occur. Hypotheses are usually written in the "if-then form": If X, then Y.

Source: Wikipedia