Modal rationalism is the claim that for any proposition p, if it is ideally conceivable that p, then there is a metaphysically possible world, W, in which p is true. If true, modal rationalism must itself be an a priori truth. Moreover, modal rationalism is true just if there are no strong a posteriori necessities. But are there any strong necessities? In this paper, I set out a transcendental argument to show that there cannot be any, because they are not genuinely conceivable. I argue that if it were ideally conceivable that there are strong necessities, then it would be impossible for us to have any modal knowledge of the world. Given that we do have some modal knowledge of the world, it follows that strong necessities are not ideally conceivable and therefore that modal rationalism itself is an a priori truth.

中文翻译：

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模态理性主义的先验真理

模态理性主义主张，对于任何命题 p，如果可以理想地想象 p，那么存在一个形而上学的可能世界 W，其中 p 为真。如果是真的，模态理性主义本身就必须是一个先验真理。此外，模态理性主义只有在没有强烈的后验必然性的情况下才是正确的。但是有什么强烈的必需品吗？在这篇论文中，我提出了一个先验论证来表明不可能有任何东西，因为它们不是真正可以想象的。我认为，如果可以理想地设想存在强烈的必然性，那么我们就不可能对世界有任何模态的知识。鉴于我们确实对世界有一些模态知识，因此强烈的必然性在理想情况下是不可想象的，因此模态理性主义本身就是一个先验真理。