It is necessary to observe as many pertinent facts as possible and as accurately as possible. Quantitative measurements are vital in modern science. Instruments greatly increase the scientist's power to do these things. They extend the scope of ordinary human experience. The next element in our definition of science is hypotheses and the testing of hypotheses.
Scientists generally carry on their research projects with some idea of what they expect to find.
They usually ask many questions and then, on the basis of what they already know, plus creative speculation about what they do not yet know, they attempt to devise explanations for what they have observed or to answer their questions. These explanations are called hypotheses. A scientific hypothesis is an educated guess framed to answer a question or to explain a set of observed facts. Sometimes the scientist reasons logically to form a hypothesis. At other times a scientist may arrive at a hypothesis by intuition or by an act of pure creative imagination.