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The only source of knowledge is experience.
— Albert Einstein
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Scientists use a scientific method to investigate phenomena and acquire knowledge. They base the method on verifiable observation — i.e., on replicable empirical evidence rather than on pure logic or supposition — and on the principles of reasoning.  Scientists propose explanations — called hypotheses — for their observed phenomena, and perform experiments to determine whether the results accord with (support) the hypotheses or falsify them. They also formulate theories that encompass whole domains of inquiry, and which bind supported hypotheses together into logically coherent wholes. They refer to theories sometimes as ‘models’, which often have a mathematical or computational basis.