“But it is time this state of affairs came to an end and accountability is brought into the AIT-vs.-OIT debate. AIT scholars can not be allowed to get away with this kind of compartmentalized discussions any more, where they can postulate any theory or situation to answer the objection, or the uncomfortable fact which cannot be swept under the carpet, that is before them at the moment, even when this theory or postulated situation sharply contradicts, or is totally incompatible with, what they postulate in other contexts.”

1990s, Update on the Aryan Invasion Debate, (1999)

Source: The Role of Measurement in Economics. 1951, p. 15

Introduction à l'Étude de la Médecine Expérimentale (1865)

Source: "Games with Incomplete Information," 1997, p. 136

Source: What Is This Thing Called Science? (Third Edition; 1999), Chapter 4, Deriving theories from facts: induction, p. 41.

Source: A Brief History of Time (1988), Ch. 1
Context: Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory. As philosopher of science Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation. Each time new experiments are observed to agree with the predictions the theory survives, and our confidence in it is increased; but if ever a new observation is found to disagree, we have to abandon or modify the theory.

The Doctrine of Necessity Examined (1892)
Context: When I have asked thinking men what reason they had to believe that every fact in the universe is precisely determined by law, the first answer has usually been that the proposition is a "presupposition " or postulate of scientific reasoning. Well, if that is the best that can be said for it, the belief is doomed. Suppose it be " postulated " : that does not make it true, nor so much as afford the slightest rational motive for yielding it any credence. It is as if a man should come to borrow money, and when asked for his security, should reply he "postulated " the loan. To "postulate" a proposition is no more than to hope it is true. There are, indeed, practical emergencies in which we act upon assumptions of certain propositions as true, because if they are not so, it can make no difference how we act. But all such propositions I take to be hypotheses of individual facts. For it is manifest that no universal principle can in its universality be compromised in a special case or can be requisite for the validity of any ordinary inference.

Context: Of course, we must avoid postulating a new element for each new phenomenon. But an equally serious mistake is to admit into the theory only those elements which can now be observed. For the purpose of a theory is not only to correlate the results of observations that we already know how to make, but also to suggest the need for new kinds of observations and to predict their results. In fact, the better a theory is able to suggest the need for new kinds of observations and to predict their results correctly, the more confidence we have that this theory is likely to be good representation of the actual properties of matter and not simply an empirical system especially chosen in such a way as to correlate a group of already known facts.

Session 410, Page 284
The Early Sessions: Sessions 1-42, 1997, The Early Sessions: Book 8