  Du Châtelet thinks hypotheses are useful (in addition to their providing a necessary step in scientific method) because “when a hypothesis is once posed, experiments are often done to ascertain if it is a good one, experiments which would never have been thought of without it” (IP §58). They are useful, that is, for suggesting innovative experiments. Such experiments can add plausibility to a hypothesis if the results of them indicate that the hypothesis captures the truth, but a single experiment which falsifies a hypothesis is enough to require the scientist to reject it, or at least, to reject whatever part of the hypothesis is deemed faulty, for a hypothesis “can be true in one of its parts and false in another” (IP §65). As an example to explain how this might be the case, she cites Descartes’ hypothesis of a vortex of fluid matter being the cause of the gravitational pull of bodies to the earth. As an example of her remarkable open-mindedness, she rejects the specifics of Descartes’ hypothesis in light of Huygen’s demonstrations that it does not square with observed facts, while also allowing that “it cannot be legitimately concluded that a vortex, or several vortices, conceived of in a different way, cannot be the cause of these movements” (IP §65). In this case, then, falsifying data requires that we invalidate only part of Descartes’ hypothesis.