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  The logic of scientific arguments
Taken together, the expectations generated by a scientific idea and the actual observations relevant to those expectations form what we'll call a scientific argument. This is a bit like an argument in a court case — a logical description of what we think and why we think it. A scientific argument uses evidence to make a case for whether a scientific idea is accurate or inaccurate. For example, the idea that illness in new mothers can be caused by doctors' dirty hands generates the expectation that illness rates should go down when doctors are required to wash their hands before attending births. When this test was actually performed in the 1800s, the results matched the expectations, forming a strong scientific argument in support of the idea — and hand-washing!

Scientific Idea + Expectations + Observations = Scientific Argument

components of a scientific argument
Though the elements of a scientific argument (scientific idea, expectations generated by the idea, and relevant observations) are always related in the same logical way, in terms of the process of science, those elements may be assembled in different orders. Sometimes the idea comes first and then scientists go looking for the observations that bear on it. Sometimes the observations are made first, and they suggest a particular idea. Sometimes the idea and the observations are already out there, and someone comes along later and figures out that the two might be related to one another.

Testing ideas with evidence may seem like plain old common sense — and at its core, it is! — but there are some subtleties to the process:

Despite these details, it's important to remember that, in the end, hypotheses and theories live and die by whether or not they work — in other words, whether they are useful in explaining data, generating expectations, providing satisfying explanations, inspiring research questions, answering questions, and solving problems. Science filters through many ideas and builds on those that work!
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  • Scientific arguments are logical descriptions of a scientific idea and the evidence for or against it.

  • Sometimes a scientific idea precedes any evidence relevant to it, and other times the evidence helps inspire the idea.

take a sidetrip
To learn more about the logic of scientific arguments, visit our unit on The core of science: Relating evidence and ideas.

key points
  • Forming hypotheses — scientific explanations — can be difficult for students. It is often easier for students to generate an expectation (what they think will happen or what they expect to observe) based on prior experience than to formulate a potential explanation for that phenomena. You can help students go beyond expectations to generate real, explanatory hypotheses by providing sentence stems for them to fill in: "I expect to observe A because B." Once students have filled in this sentence you can explain that B is a hypothesis and A is the expectation generated by that hypothesis.

  • You can help students learn to distinguish between hypotheses and the expectations generated by them by regularly asking students to analyze lecture material, text, or video. Students should try to figure out which aspects of the content were hypotheses and which were expectations.

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