What's the difference between a Theory and a Hypothesis?

From the letters page of New Scientist

See: Original Article

Lawrence Krauss is quite right that we need to be much clearer about the role of falsifiability in making a theory "scientific" (3 December, p 23). Despite taking mostly science subjects at school and having intelligent, motivated teachers, I reached the end of my secondary education without the concept having been mentioned once.

However, I'm not sure whether Krauss's attempt to clarify the word "theory" will do the trick. "Theory" is used both in normal speech and in science to refer to all varieties of idea, from wild speculation to well-tested systems. Krauss mentions falsifiable theories (such as Newton's theory of gravity), unfalsifiable theories that are at least aiming to be falsifiable (such as string theory) and theories which do not aim to be falsifiable (such as intelligent-design theory).

I don't think we will ever overcome the linguistic inertia that calls all of these "theories". If we want to be clearer, we should either insist on saying "falsifiable theory", no matter how cumbersome "Darwin's falsifiable theory of evolution by natural selection" may sound, or invent some new words.
From Timothy Surendonk

Krauss's recommendation that we remove the word "theory" from "string theory" is one that can only end in tears.

As he points out, it is a departure from the lay meaning of the word, and the confusion will only escalate when people hear the term used in scientifically allied fields such as macroeconomic theory, psychoanalytic theory and management theory - all with varying connection to the physical world.

Mathematical theories such as set theory, number theory and even computability theory don't even pretend to talk about the "real" world, yet we are happy to consider them to be in many ways scientific.

I think it is time we faced up to it: intelligent design, like string theory, is a theory. The pertinent issue is that it is not a very good theory.

Perhaps if we gave teachers some credit in their role as educators and recognised that children can and should develop the skill of critical thinking, then we would see that this is something actually worth teaching.
Kellyville Ridge, New South Wales, Australia
From Nigel Seel


Seen today in the "Science fiction and fantasy" section of a bookshop in London Heathrow airport, next to Dune by Frank Herbert: The Elegant Universe: Superstrings, hidden dimensions, and the quest for the ultimate theory by Brian Greene.
Andover, Hampshire, UK
From Paul Mealing

When I was studying philosophy, a lecturer told me that people often conflate the words "theory" and "hypothesis", which creates confusion, especially in relation to arguments concerning evolution and creationism. It was explained to me that a theory generates hypotheses that can be tested and that Popper's criterion of falsifiability applies to the hypotheses and not the theory. A theory that is unable to generate falsifiable hypotheses is not a scientific theory. According to this logic, when one has God's intervention as the only hypothesis to a theory (intelligent design), then it is not a scientific theory because its hypotheses are not falsifiable or testable.

String theory and all its variants are mathematical models attempting to resolve conflicts between quantum theory and relativity theory. Most science today is a combination of mathematics and empirical research, and when empirical results are thin or non-existent, mathematics becomes the only way forward, which is effectively what has happened in string theory.

String theory does generate hypotheses but we are not in a good position to test them, which is why Ed Witten said that string theory is 21st-century physics that accidentally found its way into the 20th century. You may wish to apply another moniker, but no one would suggest that string theory and ID have the same credence scientifically, if for no other reason than that one can be explored, albeit in the world of mathematics, and the other cannot be explored at all. ID (God made it so we can't explain it) is a bald statement that neither results from exploration nor generates it.

Science is foremost about exploration, and a theory that can't be explored has no currency, at least not in the scientific community. ID not only can't be explored, but it stops exploration, which is exactly what the creationists want. Despite their claims of being fair and open-minded, creationists, including ID proponents, are fiercely anti-science. They see science as humanistic, if not atheistic, inherently unethical, and the root cause of amoral policies on issues such as homosexuality, abortion and stem-cell research. They righteously believe that society will only find its moral compass when religion replaces science in children's classrooms.

One only has to look at the backlash George W. Bush has created in the US science community to appreciate how anti-science has already affected US policy and decision making, not to mention education.
Ivanhoe, Victoria, Australia
From Henry M. Harris

With all due respect to Krauss, I think his article is labouring under a false conception about language. Words do not have absolute meaning---they are context dependent. "Nerves of steel" does not mean your neurons are made of a carbon-iron alloy, and "sword of steel" does not mean your sword is hard but that it's made of the previously mentioned alloy. Likewise, "theory of the automobile engine" doesn't mean that automobile engines don't exist, while "string theory" is about something that may not exist.
Pasadena, California, US
From Crispin Piney

Krauss suggests that scientists should somehow explain to non-scientists - and especially creationists - that the term "theory" has a special meaning in science. I fear that this is doomed to failure and reminds me of Humpty-Dumpty insisting that words mean what you choose them to mean. I would reverse the approach and adopt the "it's only a theory" argument in the way the creationists apply it, and use it to encourage anti-evolutionists to experiment with the other "only a theory": that is to say the theory of gravitation. This is a valid comparison, since both gravitation and evolution can be shown to work; what is in debate is some of the fine detail of how they work.

I would therefore suggest that anti-evolutionists act courageously on their belief that any "only a theory" implies a non-existent effect and ignore Newton's theory of gravitation. Whereas it is less immediately dangerous to ignore evolution, the impact of ignoring the forces of gravity will possibly help convince them that an "only a theory" can be completely true - with the additional side effect of supporting Darwin's theory by removing a number of gravitational sceptics from the gene pool once and for all.