Using some common terms carefully and accurately in scientific speech and writing

As we begin our discussions for the term, I would like students to be very clear about how the usage of some common terms is different in everyday speech and in science. These differences, which I will explain below, are the source of a great deal of confusion when scientists speak to non-scientists, and even when scientists move from "scientific speech" to everyday conversations.

Being aware of these differences and taking the trouble to use words carefully can reduce this confusion in our own thinking as well as in communicating with others. In this course, I will expect everyone to learn these differences and use terms correctly in class, in posts on the discussion board and in the assignments.

Theory vs Hypothesis

What "theory" means in ordinary speech:
The term "theory" means a very different thing when used in everyday conversation and in science. In our day to day speech, we often use "theory" to mean a guess or unsubstantiated idea about how something works (as in "I have a theory that gremlins are hiding my car keys").

In science, we would call such a guess a hypothesis, not a theory. A hypothesis is a proposed explanation for an observation. In this case, I am proposing that the explanation for why I can't find my car keys is that gremlins are hiding them.*

The distinction between the words "Theory" and "Hypothesis" is very important because in science "Theory" does not mean "guess". I repeat, "Theory" does not mean "guess".

So, what does the word "theory" mean in science?
According to the National Academies of Sciences, "some scientific explanations are so well established that no new evidence is likely to alter them. The explanation becomes a scientific theory. In everyday language a theory means a hunch or speculation. Not so in science. In science, the word theory refers to a comprehensive explanation of an important feature of nature supported by facts gathered over time. Theories also allow scientists to make predictions about as yet unobserved phenomena".

People who don't understand this distinction sometimes dismiss ideas saying "it's just a theory" (this is very commonly used to suggest that evolution is just speculation, for example). But, when scientists speak of the theory of gravity or the theory of evolution, they don't mean that these are random untested ideas that someone came up with after too many beers.

The AAAS (American Association for the Advancement of Science), the world's largest scientific society, has this explanation of what scientists mean when they use the word "theory":
" A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world."

Because of this crucial difference in meaning, I will ask students to use the word "hypothesis" whenever they are referring to a speculation or guess about how something works.

* Note, that unfortunately, my hypothesis about gremlins is not useful in science, since it is notoriously difficult to detect gremlins. A hypothesis that cannot be shown to be wrong is of no use in science.


Proof vs. Evidence

Another word that is commonly misused (sadly, sometimes even by scientists, who should know better) is "proof".

What "proof" means in everyday speech:
In casual conversations, most people use the word "proof" when they mean that there is indisputable evidence that supports an idea.

Scientists should be wary of using the term "proof". Science does not "prove" things. Science can and does provide evidence in favor of, or against, a particular idea. In science, proofs are possible only in the highly abstract world of mathematics.

What should scientists say instead of "proof"?
Scientists should use the term "evidence" instead of the word "proof". When we test our hypotheses, we obtain evidence that supports or rejects the hypotheses. We do not "prove" our hypotheses.

While this may seem like a subtle difference, the words we use can subconsciously color our thinking. "Proof" suggests that a matter is completely settled, that we have had the last word on something.

In science, we are constantly adding to and refining our knowledge. When we have a sufficiently large body of evidence supporting an idea, we accept that idea. In the words of Stephen Jay Gould, "In science, "fact" can only mean "confirmed to such a degree that it would be perverse to withhold provisional assent."

For example, we accept that DNA is copied into mRNA which directs the synthesis of protein, because many studies have provided evidence that this is the case, and no studies have shown this idea to be wrong. So, we have a very high degree of confidence that this idea is correct. However, we remain open to the possibility that we may (and probably will) find, at some point, that there is more to the story than we understand at this moment.

Scientists are generally careful not to claim more than their evidence supports. That point was clearly made in Feynman's quote (on the first post I made in the discussion board) where he emphasizes the need to teach science in a way that makes clear what we know, how we know it, how well we know it, and what we don't understand. This in no way suggests that science is unsure or unreliable, but it reminds us that our current understanding is not the last word on the subject. Practicing scientists know this very well, but the general public is less clear on this concept, mainly because they do not understand clearly how science works. This is made worse when newspaper articles say things like "scientists have proved that....." which suggests that there is nothing more to be said about the subject.

As people trained in science, I think it is important for us to choose our words carefully, so we do not misrepresent the nature of science. Many non-scientists think that science has figured out all the answers (at least about the natural world). People who are not trained in science don't realize that answers in science may change with time, not necessarily because they are wrong, but because they are incomplete descriptions of reality and new evidence requires fine-tuning of an existing answer.

In this class, therefore, I will ask you all to be mindful of using the term evidence rather than proof.