Amphibians and the Particular-Universal Distinction

I defend a new conception of the particular-universal distinction based on considerations about what David Lewis calls 'amphibians'. I argue, first, that given the possibility of amphibians, two recently popular conceptions of the particular-universal distinction, namely the repeatability conception and the duplicability conception, are both objectionable since they are biased in one way or another. I then propose a more flexible conception that solves this problem by regarding amphibians as belonging to a sui generis sort of property distinct from what I call 'strong universals' and 'strong tropes'. Finally, I respond to some objections directed at this new account.