On the not_just_a_theory's page, I said :

"Evolution is just a theory.
But a theory isn't just an idea."

And not_just_a_theory responded :

"No, it is not "just a theory". It is A theory.
A theory is a scientific fact. A hypothesis that has been proven to be true.
It is supported by repeatable evidence which makes it a confirmed fact."

Because I'm not fluent in english, an english friend help me and wrote this for me.
If I correctly understand, I'm agree with her.



A scientific theory is not just an idea:
- It has to be coherent.
- It has to fit all know facts.
- It has to provide a framework from which these facts can be explained.
- It should allow some way of making predictions about some unknown facts.
Then, if experiments can be devised to check these facts, the theory will
gain credibility if the results of these experiments confirm the theory.

But neither is it a fact:

- A new theory may one day be formulated, which would also match all known
facts (including the ones which were discovered by the people working to
confirm the previous theory).
Example: Darwinism won over Lamarckism after advances in genetics.

- Proponents of a conflicting theory may also reformulate their theory to
match new facts.
Example: Such has been the case with Creationism vs. Darwinism. Whatever
evidence has been discovered to support Darwinism, proponents of
Creationism have argued that their God had included this so-called
evidence in his creation process, to test man's faith. With that
explanation, Creationism can neither be proven nor disproven.

The mere existence of these two mutually-excluding theories proves that a
theory should never be considered to be a fact.

Ultimately, there exists a school of thought claiming that nothing can be
considered to be a fact. The material world may not exist at all, or not
exist as we think we know it. It could be "Maya" (the big illusion), the
ground-level representation of a higher reality. This is, AFAIK, the
oldest formulation of that theory, and it is still firmly believed by some
(mostly oriental) mystics. Modern versions include the concept developed
in the movie "Matrix", which represents the known world as a computer
simulation.