Regularly you can see examples on this forum of people who do not understand that scientists use language in a specific manner different from the 'normal' man, or the theist, leading to much confusion.

I think it would be nice to discuss this topic so we can use it as a reference and maybe some people will learn something.

The scientists is so cautious, he must not believe what he is saying himself

Scientists often uses words such as 'may' or 'possibly' or 'could be' in conclusions.

This is not a linear indication of how true a conclusion is. That is how scientists write. Scientists know this and read sentences that seem ambiguous to the layman differently. They look at the context. What is the author presenting. How does this fit within current doctrine. How strong are his results. Is he trying to criticize the work of others (criticism of other work is often done very politely in articles).

I will try to find a suitable open access article to analyze at a later date.

Science has different standards of proof than everyday life. You see this stated formally in American criminal court trials. The jury must find that the defendant is guilty beyond a reasonable doubt. There may be six other people on the planet whose fingerprints are a good match for the ones found at the crime scene. That makes a one-in-one-billion chance that one of them was present. Coupled with the statistical likelihood that they live in Kyrghyzstan and five other distant locations and have no connection to the murder victim, that means there is no reasonable doubt that anyone else could have committed the murder. Yet murder convictions based on this premise are sometimes found to be incorrect. This is the reason many of us oppose capital punishment.

In science, for something to be regarded as true, it must be established beyond all possible doubt. This is more common in abstract disciplines like mathematics. Mathematical proofs are a matter of logic, not evidence, so its theories can be proven. Group theory, set theory, number theory... the word "theory" in mathematics refers to something that is a fact and will never be disproven.

Science deals with the physical world and its theories are based on evidence, not exclusively on logic. The theory of global warming, to choose one of the most controversial, is based on climatological evidence that has only been collected for a few decades--an eyeblink in the history of this planet--and on core samples from the distant past that show us the temperature and rainfall but not the reasons for them. The evidence for this "theory" is impressive and would probably convince a jury in a criminal trial, but it does not have the solidity of a mathematical theory. It is not highly likely, but it is possible that average temperatures will start to fall again in thirty years just as they did thirty years ago. The theory of evolution on the other hand, to choose another controversial example, is based on the more ample evidence of fossil records, carbon-14 dating, and DNA analysis. This evidence is overwhelming and falls way beyond the burden of proof in a criminal trial. New evidence is constantly discovered, prolific and consistent, giving no suggestion upon which to base an alternate theory. Countertheories rely entirely on non-scientific assumptions about supernatural beings, space aliens, or hypothesized fluctuations in natural laws that fail the test of Occam's Razor.

Nonetheless, when a biologist says that humans may have descended from an ancient species of chimpanzee three or four million years ago, he is just following good scientific method. Coincidences occur and humans may be descended from an ancient species of gorilla which left no fossil record. The probability that humans are descended from some more distant relative such as an orangutan is so small that it is misleading to the public to allow for it, yet scientists do allow for it because they cannot prove that a coincidence of Shakespearean proportions did not happen ten million years ago and all the fossil records are buried five miles deep. After all, one of the animals whose DNA is closest to ours is the mouse, because of the coincidence of a very slow mutation rate. We know enough about the role of those DNA components to understand that the differences in that DNA are in the very fundamental areas that make rodents more closely related than primates to the shrews, the distant ancestor of all of us, but the coincidence is still striking.

The concept of "theory" gets muddier when you bridge the gap between math and hard science. Take the "theory" of relativity. It's all about math and logic. Only a couple of experiments were required to verify it. It may be refined in the future, but it will never be disproven any more than the "theory" that two plus two equals four will ever be discarded just because we now have the concept of infinity.

I don't mind the scientists' use of the word "may." They have to be true to their principles. What angers me is when the popular media use the phrase, "Some scientists believe that..." That is bogus reporting. Science is not based on belief. Some scientists may think that the probability of something being true is greater than other scientists because the research is not complete and the peer reviews have not been done. But this does not mean that some of them "believe" in something and others do not.

All scientists believe in the scientific method.

Are you sure you mean this? This is generally held to be impossible in science.
I'd just comment on this to say that what mathematics gives is conditional truths. You can prove beyond all doubt that certain conclusions follow from certain axioms, but "absolute" truth as a concept doesn't exist in mathematics.

By the way, the term mathematicians use is "theorem"
The mathematics behind relativity doesn't automatically imply its truth. Both the special and general theories of relativity are based on assumptions which could always turn out to be false, and they need to be (and are) backed up by evidence as much as any theory in any scientific discipline. I don't know so much about the evidence in favour of general relativity, but the predictions of STR are confirmed all the time in particle accelerators.

If STR ever turns out to be false, it will probably only be seen to fail under extremely energetic or exotic conditions. Given the century of evidence behind the theory, the worst that could really happen to it is that it ends up being seen as a useful approximation to the truth under most circumstances, rather than being abandoned completely. This is what happened to classical/Newtonian mechanics - which still got us to the Moon.

Possibly, you may be correct.

Hmm. I don't know that this is wholly true. Conclusions always depend on initial assumptions, so "Scientists believe this..." is a roundabout way of saying that a certain set of initial assumptions are valid. The debate about these initial assumptions is where the science really is, I think.

Good choice, and I can use it to prove my point. The science is based on the assumption of the dynamics of carbon in the atmosphere. The debate stems from whether or not that assumption is valid or not. But based on that assumption, it is either trivial or impossible to show that humans are the cause of global warming.

This is a good idea. Perhaps we could eventually write a glossary that shows the meaning of words as scientists use them.

I will look forward to it. I hope it educates some people.

I've written about this concept on the wiki, in the article "Fact". It's apparently in basic agreement.

I believe it's meant that you must prove it beyond reasonable doubt. For example, strictly speaking, one cannot deny with 100% certainty that things will stop falling tomorrow. However, we have never observed an instance when the force of gravity changed at all; things have always fallen day after day, year after year, as long as we have been around to take note. So we have no reason to doubt that this will continue, and we can deny with 99.99999...% certainty that things will stop falling tomorrow. And those are still pretty damning odds.

To those who know better, perhaps. But we're talking about the often ignorant laymen here. And there's still the point that scientists don't "believe" in the facts they've discovered and studied in the same way a theist believes in the supernatural.