Schools and paradigms in science
Nowadays, most people think of scientists as being relatively uniform in thought and deed. They may read of a "scientific consensus" about issues like global warming, acid rain, and so forth. Any scientist who does not agree with the scientific consensus is presumably one of those mad scientists out to destroy the world or remove fluoride from the drinking water. (that is intended to be ironic).
But science wasn't always this way. Eighteenth century geologists were divided into schools, each of which had their own unique way of looking at rocks and interpreting the history of the world. The Neptunists, led principally by Abraham Werner, believed that all rocks were formed in the sea, either by deposition of sediments, or by precipitation from solution (both well-known processes at the time). By contrast, the Plutonists believed that rocks were formed from magma.
Most students of geology learn about these two schools (as well as two other competing schools--the catastrophists and uniformitarians) in introductory geology courses, but what is never discussed is the deeper philosophical significance of having these competing schools in science.
After all, we don't have competing schools in geology now. That is not to say that everyone agrees about all topics all the time--nothing could be farther from the truth (trust me on this--I go to conferences all the time). But there are no disagreements on the scale of requiring an entire school of geology which interprets all observations in one way as opposed to another school which will interpret the same observations differently. It seems impossible to have such structures in a science that is based on attempting to learn about the Earth through observation. What we have now . . . well, I'll get to that later.
The fundamental difference between geology now and geology in the 18th century is that the 18th century schools of geology were really based on formal systems. They were based on a logical system consisting of a set of irreducible statements, or axioms, which represented fundamental truths; and a series of rules of inference, which allowed new theorems to be proposed. Observations were used occasionally to justify one of these proven theorems. Anyone who accepted the axioms and rules of inference would logically move from one conclusion to another, and as the axioms were true statements, and rules of inference were designed to generate true statements from other true statements, any theorem generated by the formal system had to be true.
The difficulty in these systems is usually in the truth of the axioms. Rules of inference are almost always logical and work as desired (but see this story by Lewis Carroll for an argument against even the simplest rule of inference). As the statements were irreducible, they were unprovable. They had to be accepted on faith. Frequently, observations which disproved some theory would simply be explained away.
Why was science practiced this way? The scientific method was known at the time, and bodies such as the Royal Society strongly favoured this approach to science. My thinking is that the interpretation of geological observations was not sophisticated at the time, making the ideal approach to science impossible.
The practice of geology has changed fundamentally since then. And yet . . . you can still say there are schools in science. The only difference is that virtually everyone practices within the same school.
We call such schools paradigms. They differ somewhat from the older schools in that they are not based on formal systems--there are no axioms in which its practitioners keep faith. But a paradigm still places limits on scientific endeavour--it limits the types of questions asked; the way in which they are asked; and the means by which they are answered. In principle, any paradigm can be overturned by a single observation; but in reality overturning a paradigm is something that can take dozens of scientists decades (and oftimes professionally painful decades) to accomplish.
In geology, the plate tectonic paradigm is the framework within which field observations are fitted. Frequently there are some observations that don't agree with the paradigm as it is currently understood, but the paradigm concept is flexible enough to allow for a little bit of tinkering. The trouble may start when the inconsistencies start to do violence to the paradigm (see The Scientific Method and the Human Condition). Defenders of the paradigm will point out that there are literally thousands of peer-reviewed papers that have been published demonstrating that some local field observation can be explained by plate tectonic theory--strong support indeed. However, since the papers were written to fit the paradigm, then logically they should not be considered to be honest support for the paradigm.
The biggest paradigm of all in science is the Newtonian paradigm--the mechanistic view of the world. It is so large and pervasive that probably most scientists don't really think about it. Yet it just may be that this paradigm is beginning to shift.
The Dismal Science
Economics as a science still seems to be divided into numerous schools, each of which has varying successes in predicting economic behaviour. There are actually more schools than I had believed possible considering that all there is to economics is trying to figure out how humans are going to choose between alternatives in a resource-limited world.
The principal differences between the schools are in their axioms--in particular, each school has axioms which state which criteria are important when a group of humans has to choose between alternative courses of action. Different schools posit that humans base their choices on different criteria, or possibly weigh them differently.
For instance, some schools of economics consider only the opportunity and input costs for a project against the benefits. Other schools would add the costs to the environment of the project, and may well arrive at a different conclusion for the viability of the same project.
To argue about which of these schools is right is impossible, especially for an outsider--all you can do is choose the one which is closest to your own values.
To a geologist (me), this freedom to choose your reality makes it difficult for me to consider economics to be a science. At the same time, I see it as a logical way to make an economic decision. If, for instance, I decide to open a mine in Ghana, I have to decide which economic method to apply when I compare the benefits to the costs. I may have decided to include the environmental cost in my calculations of mine viability, and there are consequences to that decision--it limits the location of the mine and the style and scale of operations. Possibly another geologist would not consider the environmental costs, and would arrive at a different model for the mine. Yet both of these are viable alternatives within these different economic views.
Just don't expect me to consider economics to be a science.