Theory and Fact

One source of confusion about the status of the science or theory of evolution stems from the difference between the "everyday" meaning of the word "theory" and the scientific meaning the word.

Below we list some common misconceptions about the term "theory" and describe a classroom activity that can help students rethink their understanding of this term.

Misconception 1 "Evolution is 'just a theory'".

Misconception 2 "Theories become facts when they are well supported and/or proven."

There are three important misconceptions propagated in the above statements. The first statement implies that a theory should be interpreted as just a guess or a hunch, whereas in science, the term theory is used very differently. The second statement implies that theories become facts, in some sort of linear progression. In science, theories never become facts. Rather, theories explain facts. The third misconception is that scientific research provides proof in the sense of attaining the absolute truth. Scientific knowledge is always tentative and subject to revision should new evidence come to light.

Classroom Activity

“Fact-Hypothesis-Theory Word Jumble”

  1. Provide students with some examples of a theory, fact, hypothesis, and law.
  2. Discuss each example with students, focusing on whether the statement is based on evidence and under what conditions the statement is true.
  3. Ask students to organize these statements in some type of relative order, from that which they most readily accept to that which they consider most tentative.
  4. Provide students with the definitions of these terms from the National Academy of Sciences1
    • Fact: In science, an observation that has been repeatedly confirmed and for all practical purposes is accepted as “true”. Truth in science, however, is never final and what is accepted as a fact today may be modified or even discarded tomorrow.

    • Hypothesis: A tentative statement about the natural world leading to deductions that can be tested. If the deductions are verified, the hypothesis is provisionally corroborated. If the deductions are incorrect, the original hypothesis is proved false and must be abandoned or modified. Hypotheses can be used to build more complex inferences and explanations.

    • Law: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances.

    • Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

  5. Ask students to identify each of the original statements as a Fact, Hypothesis, Law, or Theory and to revisit the arrange of statements, from that which they would most readily accept to that which they consider most tentative, and make any changes deemed necessary.
  6. Did the order change? If so, how and why?

Recommended Resources:

Understanding Evolution and UC Museum of Paleontology

From the PBS Evolution series "Evolving Ideas: Isn’t Evolution Just a Theory?"

"Theory in Theory and Practice" (pdf) by NCSE's Glenn Branch and Louise Mead Evol Edu Outreach 1:287-289, 2008

"Evolution as Fact, Theory, and Path" by Ryan Gregory, Evo Edu Outreach 1:46-52, 2008.

"The Role of Theory in Advancing 21st Century Biology", a special brief report from the National Academies of Science, 2007 (pdf)