ABSTRACT
In order to accept a hypothesis on the grounds that it is the best explanation of the evidence, one must know what other hypotheses compete for evidential support with the first hypothesis. But the principles for determining when hypotheses compete are obscure and represent a currently unsolved problem for this form of inference. Competing hypotheses need not contradict each other. A defender of inference to the best explanation as a distinctive form of inference will not want to identify competing hypotheses with hypotheses that are jointly highly improbable. Relying on probabilities to solve this problem would be to put the cart before the horse, since the idea behind taking inference to the best explanation to be a distinctive form of inference is that we use inference to the best explanation to determine probabilities, not the reverse Furthermore, it does not work to rely on a failure by the “hypothesis generator” to generate anything but competing hypotheses, because that just pushes the problem over to the hypothesis generator. Anyway, noncompeting hypotheses often have to be considered and therefore have to be generated Whether there is competition between two hypotheses seems to depend at least in part with whether one might be used to “fill out” the other without leading to a major change in the explanation. But it remains unclear how to distinguish “filling out” an explanation from changing it.
