Hence it could never be - and never was - improved upon through experiment. The Enlightenment was at root a philosophical change. The physicist Galileo Galilei was perhaps the first to understand the importance of experimental tests (which he called cimenti, meaning 'trials by ordeal') as distinct from other forms of experiment and observation, which can more easily be mistaken for 'reading from the Book of Nature'.
Testability is now generally accepted as the defining characteristic of the scientific method. Popper called it the 'criterion of demarcation' between science and non-science. Nevertheless, testability cannot have been the decisive factor in the scientific revolution either.
Contrary to what is often said, testable predictions had always been quite common. Every traditional rule of thumb for making a flint blade or a camp fire is testable. Every would- be prophet who claims that the sun will go out next Tuesday has a testable theory.
One statement of it is 'Do not multiply assumptions beyond necessity. ' However, there are plenty of very simple explanations that are nevertheless easily variable (such as 'Demeter did it'). And, while assumptions 'beyond necessity' make a theory bad by definition, there have been many mistaken ideas of what is 'necessary' in a theory.
Instrumentalism, for instance, considers explanation itself unnecessary, and so do many other bad philosophies of science, as I shall discuss in Chapter 12. When a formerly good explanation has been falsified by new observations, it is no longer a good explanation, because the problem has expanded to include those observations. Thus the standard scientific methodology of dropping theories when refuted by experiment is implied by the requirement for good explanations.
The best explanations are the ones that are most constrained by existing knowledge - including other good explanations as well as other knowledge of the phenomena to be explained. That is why testable explanations that have passed stringent tests become extremely good explanations, which is in turn why the maxim of testability promotes the growth of knowledge in science. Conjectures are the products of creative imagination.
If some of those people consequently create more knowledge than they otherwise would have, and become happier than they otherwise would have been, then part of the 50 per cent of happiness that was 'genetically determined' in all previous studies will no longer be so. The interpreters of the study may respond that it has proved that there can be no such book! Certainly none of them will write such a book, or arrive at such a thesis. And so the bad philosophy will have caused bad science, which will have stifled the growth of knowledge.
Notice that this is a form of bad science that may well have conformed to all the best practices of scientific method - proper randomizing, proper controls, proper statistical analysis. All the formal rules of 'how to keep from fooling ourselves' may have been followed. And yet no progress could possibly be made, because it was not being sought: explanationless theories can do no more than entrench existing, bad explanations.
It is no accident that, in the imaginary study I have described, the outcome appeared to support a pessimistic theory. A theory that predicts how happy people will (probably) be cannot possibly take account of the effects of knowledge-creation. So, to whatever extent knowledge-creation is involved, the theory is prophecy, and will therefore be biased towards pessimism.
Thus they also deny that other great truth that I suggested we engrave in stone: problems are inevitable. A solution may be problem-free for a period, and in a parochial application, but there is no way of identifying in advance which problems will have such a solution. Hence there is no way, short of stasis, to avoid unforeseen problems arising from new solutions.
But stasis is itself unsustainable, as witness every static society in history. Malthus could not have known that the obscure element uranium, which had just been discovered, would eventually become relevant to the survival of civilization, just as my colleague could not have known that, within his lifetime, colour televisions would be saving lives every day. So there is no resource-management strategy that can prevent disasters, just as there is no political system that provides only good leaders and good policies, nor a scientific method that provides only true theories.
But there are ideas that reliably cause disasters, and one of them is, notoriously, the idea that the future can be scientifically planned. The only rational policy, in all three cases, is to judge institutions, plans and ways of life according to how good they are at correcting mistakes: removing bad policies and leaders, superseding bad explanations, and recovering from disasters. For example, one of the triumphs of twentieth-century progress was the discovery of antibiotics, which ended many of the plagues and endemic illnesses that had caused suffering and death since time immemorial.