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Practices of Science: Opinion, Hypothesis & Theory

NGSS Science and Engineering Practices

An opinion is a statement describing a personal belief or thought that cannot be tested (or has not been tested) and is unsupported by evidence. A hypothesis is usually a prediction based on some observation or evidence. Hypotheses must be testable, and once tested, they can be supported by evidence. If a statement is made that cannot be tested and disproved, then it is not a hypothesis. Sometimes it is possible to restate an opinion so that it can become a hypothesis.


A scientific theory is a hypothesis that has been extensively tested, evaluated by the scientific community, and is strongly supported. Theories often describe a large set of observations, and provide a cohesive explanation for those observations. An individual cannot come up with a theory. Theories require extensive testing and agreement within the scientific community. Theories are not described as true or right, but as the best-supported explanation of the world based on evidence.


SF Fig. 7.9. Alfred Wegener first proposed the idea of continental drift.

Image courtesy of Deutsches Dokumentationszentrum für Kunstgeschichte - Bildarchiv Foto Marburg, Wikimedia Commons

German-born geophysicist Alfred Wegener is credited with proposing a hypothesis of continental drift in the late 1800’s, but it was not until the 1960’s that his concept became widely accepted by the scientific community. Part of the problem Wegener faced in presenting his hypothesis of continental drift was that he did not have a sufficient evidence to be able to propose the mechanism of continental movement. Wegener suggested that the continents moved across the ocean floor, but the lack of disturbance on the ocean floor did not support this part of his hypothesis. The elevation of continental drift to the status of a theory came largely from evidence supporting new ideas about the mechanism of plate movement: plate tectonics. It was only over time, as more scientists evaluated and added to Wegener’s original hypothesis, that it became widely accepted as a theory.


Question Set
  1. Identify which of the following are hypotheses and which are opinions. Rephrase the opinions as hypotheses.
    1. Arc-shaped island chains like the Aleutian Islands are found at subduction zones.
    2. Dinosaurs were mean animals.
    3. Mammals are superior to reptiles.
    4. An asteroid impact contributed to the extinction of dinosaurs.
    5. Science can answer any question.
    6. The climate on Antarctica was once warmer than it is now.
    7. The center of the earth is made of platinum.
  2. You have a hypothesis that the land near your school was once at the bottom of the ocean, but due to continental movement, it is now miles inland from any water source. How would you test your hypothesis? What evidence would you use to support your claim?
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.