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About this quote

What does it mean?
A true theory must not only explain known phenomena but also predict new ones.
In plain terms
Good theories explain and forecast what we haven't yet seen.
What can you take from it?
Test theories by their predictive power.

Where it applies

  • climate modeling
  • medicine

Putting it to work

  • designing experiments
  • building predictive models

Questions to consider

  • What makes a prediction valuable?
  • How to handle failed predictions?

Another view

Some useful theories may lack immediate predictive success.

More from William Whewell

  1. The catastrophist constructs theories, the uniformitarian demolishes them.

    Permalink to quote #10
  2. In art, truth is a means to an end; in science, it is the only end.

    Permalink to quote #9
  3. Man is the interpreter of nature, science the right interpretation.

    Permalink to quote #8

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