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We distinguish between factual statements and theories. If
the path from a statement to verifiable predictions is short and
uncontroversial, we call it factual. A theory is a statement
which can generate a wide scope of predictions, but only through
some intermediate steps, such as reasoning, computation, the use
of other statements. Thus the path from a theory to predictions
may not be unique and often becomes debatable. Between
the extreme cases of statements that are clearly facts
and those which are clearly theories there is a whole
spectrum of intermediate cases.
Top-level theories of science are not deduced from
observable facts; they are constructed by a creative act, and their
usefulness can be demonstrated only afterwards. Einstein wrote:
"Physics is a developing logical system of thinking whose
foundations cannot be obtained by extraction from past experience
according to some inductive methods, but come only by free fantasy".
The statement of the truth of a theory has essentially the
same meaning as that of a simple factual judgment: we refer to
some experience which justifies, or will justify,
the decision-making on the basis of this statement.
When this experience is in
the past we say that the truth is established.
When it is expected in the future we say it is hypothetical.
There is no difference of principle between factual
statements and theories: both are varieties of models of reality which
we use to make decisions. A fact may turn out to be an illusion,
or hallucination, or a fraud, or a misconception. On the other
side, a well-established theory can be taken for a fact. And we
should accept critically both facts and theories, and re-examine
them whenever necessary. The differences between facts
and theories are only quantitative: the length of the path
from the statement to the production of predictions.