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Student Roadmap - Arguing from Evidence

Convincing Arguments Come from Evidence and Reasoning

Scientists must learn to argue well

When scientists have a new idea, they have to present a convincing argument about why the new idea is better than older ideas. If their argument and the evidence they use to back it up are convincing, it can get through the peer-review process, other scientists start to use the new idea in their own work, and soon it becomes an “accepted” idea that is shared among scientists and taught to science students. Maybe in another ten years another new idea that has lots of evidence to back it up will replace that idea, and the cycle repeats itself.

Scientists are always coming up with new experiments to test the accepted ideas. New data and new evidence are turned up all the time. When the new data doesn’t turn out as expected using accepted ideas, scientists get excited because it an opportunity to develop a new idea and use the unexpected data to challenge the accepted idea and propose and argue for something new.

Sometimes a new idea is revolutionary, but more often it’s just refining or changing the accepted idea a little bit.

How Science Argument is Different than Debate

Arguing in science is a little different than other arguments you might be familiar with. In science argument:

  • The focus isn’t on winning the debate or selling your idea to an audience. It’s about discussing, sharing, and learning.
  • Science arguments focus on ideas, so it’s the ideas that get challenged, not the people that express them.
  • Scientists realize that an idea must fit with the most valid observations possible. While scientists may strongly defend a particular theory, if new evidence is discovered that doesn’t support their theory, they have three options:
    1. challenge whether the new evidence is valid based on a critique of the experiment that was done to collect it (“but you only exposed those seeds to heat…they had plenty of water, so how can you say that your conclusion applies to seeds growing the Southwest?”)
    2. change their theory and their thinking to include the new evidence
    3. accept that their idea is limited ("OK, so maybe it works one way in sunflowers and another way in peas”).
  • It’s important to keep an open mind. Just because you start out on one side of an argument doesn’t mean it’s not OK to be convinced that there is a better idea to explain the facts. It’s all about putting together a theory that explains the most. Maybe that’s a combination of several ideas that are being argued. You can change your mind at any time, and you can throw in a new idea at any time.
  • Science arguments also consider alternate possible explanations.

How Science Argument Fits with Investigation

Argument happens all throughout a science investigation. Scientists argue about:

  • The best way to set up an experiment.
  • Whether the data collection is done in a valid way.
  • How graphs and charts should be put together
  • What the data mean, which data can be used as evidence
  • How strong and how important the conclusions are

Some of the argument is to decide if the data are reliable and valid. All information collected during an investigation isn’t necessarily evidence. For example, some data may not directly answer the research question. Some observations or measurements may not be accurate, perhaps due to equipment problems or errors in collecting the data. In cases like these, the data don’t count as evidence.

Other arguments then are used to decide if the experimenter’s ideas or conclusions are the best way of explaining the data.

Very often argument sends experimenters back to the field or laboratory to collect more data that will help make a case for one idea or another. One of the best ways to convince other scientists about a certain idea is to figure out a simple experiment that tests two ideas against each other.

“If A idea is right, then we should see B.” “But if X idea is right, we should see Z instead.”

Then both scientists argue about the details of a fair test

“But we have to use sunflowers, because peas might be different…” “And we have to expose the plants to both heat and dry to make it most like the Southwest…”

And then both scientists go back and try a similar experiment and see what happens. If they both get Z, then idea X is probably right.

Just so stories

In the science community explanatory stories without evidence to back them up are sometimes referred to as “Just So Stories” after Rudyard Kipling’s collection of stories (The Elephant's Child is a good example). The criticism is that without evidence, the nicest story — even if it makes a lot of sense and seems like it could be true — is still only nice literature, not scientifically convincing.

How Do You Construct a Scientific Argument and Defend It?

  • Base your arguments on evidence (data, observations). Having a good story that explains how things work or happen is important, but can’t stand alone without evidence. Back up your story with evidence.
  • Be sure the evidence is valid (take a close look at methods used to collect the evidence and be prepared to defend methods for evidence you use in your argument).
  • If someone challenges your idea by introducing evidence that doesn’t fit, you need to take that seriously and explain why it’s an exception, why the evidence isn’t valid, or change your idea to include that evidence.
  • Debate ideas, not people. Try to keep the argument from becoming personal.