可能世界の現実性

Abstract

We recognize that natural laws have the reality beyond facts such as to make truth of counterfactual conditionals like "If it were not for the atmosphere, the cannonball would fly farther." David LEWIS claims that possible worlds exist in the same way the actual world exists. He extends the field of facts and on this basis he explains the truths of such counterfactuals, then causality etc. For his success in explanation, I think, possible worlds ought to exist in the determined manner. But as he thinks the measure of similarity of possible worlds to be subjective, there rises a problem that the truths of counterfactuals are influenced by this subjectivity. The reality of natural laws should be understood not by means of the reality of possible worlds but on a basis of the priority of thought over facts. That is to say, we should think that the world comes into being only by being understood along our system of knowledge including natural laws.