Realism and Instrumentalism in Science
Introduction: realism in science
It seems obvious to say that science makes discoveries. Modern science has discovered the existence of planets, bacteria, viruses, cells, synapses and innumerable species of plants. And if these are all scientific discoveries then the objects clearly must exist. That seems obvious. This obvious truth can be expressed by saying that the appropriate attitude towards science is "realism". This means, firstly, that scientific theories are sometimes true, and secondly, that the objects referred to by the true scientific theories planets, bacteria and so on do actually exist. Of course, not all the objects referred to by scientific theories do actually exist since some scientific theories are false. For instance, before the 18th century it was thought that combustible substances such as phosphorous contained large quantities of a substance known as "phlogiston". Now we know better. Phlogiston does not exist. Thus to be a realist with regard to scientific theories is to believe that scientific theories can be true, and that the true theories give a more complete description of the physical world. The objects referred to by the true scientific theories do exist. Not that it matters too much but realism is probably the most widely held or "commonsense" view of science. So is there anything wrong with realism? In order to answer this question, consider some more scientific objects - electrons, neutrinos, photons, gravitational fields, quarks and black holes. According to modern science these objects, also, do actually exist but here there may be some misgivings. Objects such as neutrinos, photons or gravitational fields can never actually be observed. Neutrinos, electrons and other sub-atomic particles do leave tracks in cloud chambers, but to observe the tracks of an electron is not the same as directly observing an electron. Similarly, to observe a polar bear's tracks in the snow is not the same as observing the polar bear. Moreover, objects such as electrons have both wave and particle properties - there is no clear and consistent understanding of such notions. And also, as the American philosopher of science Ernest Nagel has pointed out, there are a number of scientific concepts which don't refer to any actually existing things ideal gases, perfect elasticity, limiting velocities and point particles. These notions, Nagel claims, are theoretically convenient but don't refer to anything physically real. They are sometimes called "models" which, though an aid in understanding, do not actually exist. For instance, according to the kinetic theory of matter an ideal gas is made up of perfectly elastic balls in random motion. Nagel's point is that even though this notion of an ideal gas may help explain certain facts about the temperature and pressure of gases, ideal gases do not exist. Thus realism is not quite as certain as it first may have appeared. Nagel's suggestion is that realism should be abandoned in favour of a different view of science "instrumentalism".
Instrumentalism
According to Nagel, the central claim of instrumentalism is that a scientific theory is a rule, principle or calculating device for deriving predictions from sets of observational data. A scientific theory is an instrument or function where the input is a set of observations and the output is another set of observations the predictions. Nagel gives the following example:
"
the theory that a gas is a system of rapidly moving molecules is not a description of anything that has been or can be observed. The theory is rather a rule which prescribes a way of symbolically representing, for certain purposes, such matters as the observable pressure and temperature of a gas; and the theory shows among things how, when certain empirical data about a gas are supplied and incorporated into that representation, we can calculate the quantity of heat required for raising the temperature of the gas by some designated number of degrees (ie. we can calculate the specific heat of the gas.)" (Nagel, p. 129)
Thus instrumentalism, as opposed to realism, denies that a scientific theory is a literal description of the world. For instrumentalists the kinetic theory of matter is no more than a convenient device or rule for making certain calculations and predictions about gases (and liquids, etc). We should not, therefore, think that the world literally contains molecules. Similarly, for the instrumentalist the world does not actually contain electrons, protons, gravitational fields and so on. These are often called "theoretical entities", and instrumentalism can be summarized by saying "There are no theoretical entities". An instrumentalist views the theoretical terms "electron" and "photon" to be just like the terms "equator" or "kilometre." To partition the earth using lines such as the equator, parallels of latitude and meridians of longitude is convenient for many purposes (e.g. time zones), but despite their convenience these lines are imaginary nevertheless.
Some problems with instrumentalism
- Scientists search long and hard for evidence which would confirm and maybe falsify scientific theories. This would seem to be pointless if theories are no more than calculating devices.
- Instrumentalism seems to undermine the explanatory function of scientific theories. After all, if electrons don't really exist, how can they actually produce tracks in a cloud chamber or explain the facts of electricity? Or how can genes explain the facts of heredity if genes don't exist?
- The instrumentalist claim that theoretical entities don't exist seems to rest on a very sharp distinction between theoretical and non-theoretical entities. Quarks, electrons and photons may be clear examples of theoretical entities. But what about planets, bacteria, viruses, quasars, radio waves? Can't these be observed, at least in some sense? And if so, why not say that they exist? Isn't the theoretical/non-theoretical distinction dependent on how advanced the current observational techniques at a scientist's disposal? What is a theoretical entity at one time may become directly observable at a later time. Think of advances in microscopes, radio telescopes and X-ray crystallography. Therefore if the theoretical/non-theoretical distinction is blurred, there seems no reason to deny the existence of objects such as quarks and electrons.
Some questions
- The dispute between realists and instrumentalists concerns the existence of certain types of entities. But how do we tell whether or not something exists? A usual test is observability if we can observe X then X exists. By this criterion lions exist but unicorns do not. Will the observability criterion work in the case of realism versus instrumentalism? As mentioned earlier, there is a problem with entities such as sub-atomic particles because they don't seem to be directly observable. Is there a better criterion than observability? Perhaps: an object X exists if X is referred to in well established physical laws and theories. For example, according to this criterion genes exist since these are referred to in the laws and theories of population and molecular genetics. According to this criterion, electrons and quarks exist but phlogiston and the aether do not.
- If instrumentalism were true, then what would be the consequences for the notion of scientific explanation? As mentioned earlier, if there (really) are no gravitational fields, then what becomes of the explanation of the facts relating to escape velocity in terms of the earth's gravitational field? Does this matter? If accurate predictions can be made on the basis of scientific theories, then who cares about explanation and the existence of theoretical entities?
Reference
E. Nagel, The Structure of Science.
R. Neurath
