Karl Popper

The second reading for Philosophy of Science this semester is Science: Conjectures and Refutations. It's a beautiful thing. Now, there are some problems with defining 'scientific' solely in terms of falsifiability, but it is certainly an important feature to note in any theory. I particularly liked that what brought Popper to use that as a criterion was that two competing psychological theories (those of Freud and Adler) were sufficiently vague as to be able to explain any conceivable set of behaviors. He had at first been impressed with their seemingly endless lists of confirmations...until he noticed that there seemed to be no behavior that could be taken as falsifying either one. The link above is to the full article, but I just thought I'd post his summary list. Closely related: Confirmation Bias. I've bolded a few of the parts that I find most significant.

1. It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations.

2. Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory — an event which would have refuted the theory.

3. Every "good" scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.

4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.

5. Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks.

6. Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory. (I now speak in such cases of "corroborating evidence.")

7. Some genuinely testable theories, when found to be false, are still upheld by their admirers — for example by introducing ad hoc some auxiliary assumption, or by reinterpreting the theory ad hoc in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status. (I later described such a rescuing operation as a "conventionalist twist" or a "conventionalist stratagem.")

One can sum up all this by saying that the criterion of the scientific status of a theory is its falsifiability, or refutability, or testability.

Shorter Popper: A scientific approach to any idea is to throw rocks at it and see if it breaks. If you throw marshmallows, you're doing it wrong.

Redefinition is trickier. There are cases where the breaks simply indicate the limits of an idea, rather than its overall refutation, and it might be able to be modified to account for those breaks. There are also cases where lunatics liberally apply duct tape and declare it as good as new.