Science does not begin with facts and then construct theories out of them. Nor does science begin with theories and then just find facts that would confirm them. Both these conceptions conceive of science as though it were a discourse that was completely context free. In the first case, facts are simply available as though they were waiting for interpretation of a specific kind, and in the second case, theories are simply open to facts as though there were no inertia or hindrance to the smooth progress of science from one theory to the next, each equally open to the possibility of falsification.
The first philosopher to take the idea of context or background to scientific activity seriously was Thomas Kuhn. Loosely characterised this approach might be called ‘historical’. What does it mean to treat science as though it were part of history rather than outside of it? It means first of all to take scientists seriously. It is to treat what they do the same way that we would analyse the thoughts and actions of French peasants or the 13th century or a military general in the 20th. First of all to record scientific achievements correctly (who thought of what at what time), and secondly to examine exactly how scientists come up with their theories in relation to the material they were investigating. What it certainly is not is the importation of philosophical theories from the outside (like verification or falsification) followed by squeezing the scientific activity to see whether it would fit these ideal models.
However much the logical positivists and Popper might differ, they both have the same idealised view of science: there is a sharp difference between theory and observation; knowledge is cumulative tending towards a true understanding of the universe; science is deductive; the language of science is precise and science is unified; the key question of the philosophy of science is legitimacy and validity, rather than the contingency of discovery. Against all the suppositions Kuhn puts forward exactly the opposite: there is no sharp difference between observation and theory; knowledge is discontinuous; science is not a tight deductive structure; scientific concepts and not precise; nor is science unified; context is important and science is historical and temporal.
At the heart of the idealised picture of science is scientific progress. This is the view that science is leading to ever increasing knowledge about the universe and that finally one day we will have a theory of everything, and I suppose, science can come to end, because there will be no more questions that need to be answered. So first of there are pre-scientific theories of the universe that we find in the religious and mythical texts (like Genesis), and then we get the first science, Aristotelianism (though this is a really a mixture of science and occult explanations), then Newtonism (which is the first science proper) and then finally in our times, Einsteinian science which is a response to the crisis that befell Newtonism. One imagines that sometime in the future, though one can never tell, there will be fourth science that will replace Einstein, but only because it contains more truth and is close to the universe as it really is.
There are two problems with this image of science. One is temporal and the practical. First of all it has a conception of time, where the past is merely a stepping stone to the present but the past has no meaning in itself. For how can we measure the progress of science in this sense unless we imagine an end towards which it is moving and this end is supposed to be an advance on the past? But how can we know that this advance is real unless we can stand outside of time and measure it? Is it not really the case that past is not the stepping stone to the future, but that we judge the past from the vantage point of the present, and in looking back, project a false teleology back into the past? In terms of the past itself, there were numerous possibilities and the present that we now occupy did not have to occur. Equally the present that we now stand in has infinite possibilities, so we cannot know what the future will be.
In terms of the practice of science, we also know that his temporal picture of progress is false. This is what Kuhn discovered when he did his own historical research. Rather than the history of science demonstrating that each scientific period progressed into the next one moving to ever greater level of truth and closing the distance between discourse and reality, we find that it is discontinuous and non-cumulative and that there is no reality out there by which we could measure the relative truths of each discourse because reality itself is a creation of discourse and not its external validation.
What does it mean to say that the history of science is discontinuous rather than continuous, non-cumulative rather than cumulative? Let’s go back to the image of progress where science moves smoothly from Aristotle, to Newton, to Einstein. What is left out in this description is the gaps or spaces between each scientific theory (or what Kuhn calls a paradigm, because it is more than just a theory) and it can leave this gaps out because the fantasy of some ultimate truth which is where reality and discourse are the same. As soon as we leave this fantasy behind, and realise that it too is a creation of a discourse (in this case metaphysics), then we can see that there is no transition of one to the other. Rather, they are separate or incommensurable. They belong to different worlds.
Again this is visible when we actually study the history of science, rather than project our own view of progress upon it. What we get instead of single continuous line is line of breaks: Aristotle, Newton and Einstein. What then causes these breaks? Why don’t we just go from one science to another in an endless progression towards the truth? The answer for Kuhn is to be found in psychology and sociology and not in the philosophical image of science as a universal method.
The new picture we have of science is now as follows: first we have pre-science – normal science – crisis or revolution – new normal science – new crisis (Chalmers 1999, p.108). When at first science begins to emerge we don’t have a collection of facts or theories that explain facts, rather we have a competition between many theories (Chalmers gives the example of the state of optics before Newton). Gradually like a different scientists will be attracted to the one explanation. What is important is that the reason for this attraction will not just be scientific or rarely just scientific. It will be psychological and sociological. As more and more scientists come on board, what is in the state of chaos will coagulate into a paradigm. Only at that point will normal science be possible (the kind of science that Popper and the logical positivists describe). But even a paradigm, which makes normal science possible, is not made up of merely theories and observations. Like Newtonian mechanics, it is constructed from fundamental laws and theoretical assumptions, standard techniques and methods of investigation, general rules about exceptions and application to reality and most importantly of all a kind of world view or metaphysics which will unify all of this together (in Newtonism, that we exist in an infinite deterministic universe).
Rather than anomalies, as Popper would have us believe, being antithetical to normal science, it can quite happily accept them as long as they don’t attack the fundamentals of the paradigm. Everyone can get happily to work devising their experiments and putting in their grants and anyone who goes against the status quo can be banished to the outer darkness. The paradigm is reinforced by the institutions themselves. If you don’t follow the paradigm you won’t get the grant money, and anyway the educations of young scientists make sure that they follow the paradigm. This is clearly what Kuhn saw when he first looked into the history of science as a practicing scientist: young scientists were taught the idealised image of science that had nothing at all to do with the history of science at all.
So why do paradigms fall? Why are revolutions inevitable? This is because of the anomalies. Because no discourse can close the gap between itself and reality, there will always be the nagging doubt that something is not being explained by the paradigm. As more and more money and experiments are thrown at these anomalies, cracks begin to appear in the scientific establishment. Thus a normal science begins to take the form of the pre-science. Rather than scientists doing experiments, they start having ideas and hypothesis. Some might be said to be cranks and fools, but gradually they begin to attract other scientists. Again Kuhn is clear that the reason for this cannot be scientific or logical, because there is nothing in one paradigm that would justify the leap to another, for there is no commensurability that would link them together, such that one might say that one is truer than the other. The reasons are psychological and sociological. As more and more are attracted to this new science, gradually a new paradigm is born and the whole process repeats itself. We get a new normal science, where again people can happily devise their experiments, apply for grants and get promotion. Until of course the cracks start appearing again.
Although this appears to be an accurate representation of what scientists do, there is a fundamental problem with it. If we are to give up the image of science as the progress towards a truth in which the distance between discourse and reality is progressive closed, for a discontinuous series of closed paradigm, then does this make scientific truth relative? We can distinguish normal science from pseudo-science because of how paradigms work (the difference between astronomy and astrology), but that does not make science itself any truer. Can we say that Einstein, for example is truer than Newton? We want to feel that this is the case, but Kuhn’s principle of incommensurability will not let us do so.
Chalmers, A.F., 1999. What is this Thing Called Science?, St. Lucia, Qld.: University of Queensland.
Sharrock, W.W. & Read, R.J., 2002. Kuhn : Philosopher of Scientific Revolution, Cambridge: Polity.
 He might have been the first American philosopher to take this idea seriously. In France, this was the dominant view of science (Sharrock & Read 2002, p.1).
 It is science (think for example of evolution) itself that would make us suspect such teleological arguments.