1.2: What is the difference between a fact, a theory and a hypothesis?
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This article is from the Scientific Skepticism FAQ, by Paul Johnson Paul@treetop.demon.co.uk with numerous contributions by others.
1.2: What is the difference between a fact, a theory and a hypothesis?
In popular usage, a theory is just a vague and fuzzy sort of fact.
But to a scientist a theory is a conceptual framework that *explains*
existing facts and predicts new ones. For instance, today I saw the
Sun rise. This is a fact. This fact is explained by the theory that
the Earth is round and spins on its axis while orbiting the sun. This
theory also explains other facts, such as the seasons and the phases
of the moon, and allows me to make predictions about what will happen
tomorrow.
This means that in some ways the words "fact" and "theory" are
interchangeable. The organisation of the solar system, which I used as
a simple example of a theory, is normally considered to be a fact that
is explained by Newton's theory of gravity. And so on.
A hypothesis is a tentative theory that has not yet been tested.
Typically, a scientist devises a hypothesis and then sees if it "holds
water" by testing it against available data. If the hypothesis does
hold water, the scientist declares it to be a theory.
An important characteristic of a scientific theory or hypotheis is
that it be "falsifiable". This means that there must be some
experiment or possible discovery that could prove the theory untrue.
For example, Einstein's theory of Relativity made predictions about
the results of experiments. These experiments could have produced
results that contradicted Einstein, so the theory was (and still is)
falsifiable.
On the other hand the theory that "there is an invisible snorg reading
this over your shoulder" is not falsifiable. There is no experiment
or possible evidence that could prove that invisible snorgs do not
exist. So the Snorg Hypothesis is not scientific. On the other hand,
the "Negative Snorg Hypothesis" (that they do not exist) is
scientific. You can disprove it by catching one. Similar arguments
apply to yetis, UFOs and the Loch Ness Monster. See also question 5.2
on the age of the Universe.
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