  So Du Châtelet takes an extremely friendly view of the role of hypothesis in scientific reasoning. Still, wary of those who make bad use of hypotheses, Du Châtelet puts strict limits on their use. A hypothesis must “not only [explain] the phenomenon that one had proposed to explain with it, but also that all the consequences drawn from it agree with the observations” (IP §58). Herein, we have the idea that a good hypothesis will explain a plethora of effects including many not originally under investigation. Du Châtelet believes that the more such effects that can be explained (as well as the more experiments performed which turn out as predicted by the hypothesis), the more probable the hypothesis is. Indeed, Du Châtelet makes the very strong claim that “hypotheses finally become truths when their probability increases to such a point that one can morally present them as certain” (IP §67), though the psychological context of the passage (“as a very great degree of probability gains our assent, and has on us almost the same effect as certainty”) indicates that a highly probable hypothesis is merely highly probable and not strictly true, and  that Du Châtelet’s considered position is “that hypotheses become the poison of philosophy when they are made to pass for the truth” (IP, Avant-Propos  VIII)[23]. According to Du Châtelet, part of the scientist’s job is to “have certain knowledge of the facts that are within our reach, and to know all the circumstances attendant upon the phenomena we want to explain… for he who would hazard a hypothesis without this precaution would run the risk of seeing his explanation overthrown by new facts that he had neglected to find out about” (IP §61). So the scientist must become acquainted with many empirical facts so as to ensure that she is not ignorant of potentially falsifying data (IP §64).