 Second, perfectly natural properties and relations are, Lewis thinks, non-modal. What, exactly, this means will need to come in for more discussion. For the moment, we can take it to mean roughly this (though trouble for this characterization quickly arises): the instantiation of a perfectly natural property by one (fundamental) particular, or of a relation by several, places absolutely no constraints of a logical or metaphysical kind on the instantiation of any other perfectly natural property or relation by that or any other particular or particulars.