[jballanc]

Fact: In science, an observation that has been repeatedly confirmed.

Law: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances.

Hypothesis: A testable statement about the natural world that can be used to build more complex inferences and explanations.

Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

(Source: http://arstechnica.com/science/2006/08/5164/)

Edit:

How it works...

"Massive objects are attracted to each other by the force of gravity." == Scientific Fact.

"Objects in motion remain in motion. For every force there is an equal an opposite reaction. Force is mass times acceleration." == Scientific Law (Newton's Laws of Motion).

"The bending of space under the influence of gravity can cause light to curve around massive objects." == Scientific Hypothesis (Verified by Eddington's 1919 solar eclipse observations).

All of the above (and a whole lot more) put together == General Theory of Relativity.

[aortega]

>Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

...that can be wrong and often are replaced by better theories as more tests and better explanations came out.

Science is based in doubt. If you are too sure of a scientific theory, you are missing what science really is about and what you need is religion.

[jballanc]

Falsifiability is a feature of every element of science. Something that is not falsifiable isn't science. Period.

But a Theory is not a guess. It is a framework built from individual pieces, some of which may be hypotheses (effectively guesses) that have been tested and found to hold within the larger structure of that framework.

[aortega]

If you are based in individual pieces that may be effectively guesses, how you are not also a guess?

[jballanc]

Try formulating your question again, but this time don't leave out the part where I wrote "that have been tested and found to hold".

[chc]

Because you have been tested. The term "guess" implies lack of good grounding.

[BlackDeath3]

The reason that theories are not referred to as "guesses" is because there is, in theory (pun intended), an enormous chasm of evidence between a theory, and a guess/hypothesis.

Nothing is known with absolute certainty. What is the point is referring to everything as a "guess" simply because it isn't known for certain? Context is important here.

[saraid216]

Fallibility doesn't make it a "guess".

[aortega]

Funny you mention the Newton's Laws of Motion, that's the most famous theory demonstrated to be totally wrong.

It was a very good guess though.

[jballanc]

sigh ...take a moment to re-read what I wrote. Then take a moment to re-read what you wrote.

Newton's LAWS of Motion are not a THEORY. They are a descriptive generalization about how gravitation behaves under stated circumstances. Those circumstances being slow speeds and large masses. In those circumstances, they are not wrong. They are a generalization. The THEORY of General Relativity contains Newton's LAWS of motion as a part of the overall framework.