 The fourth constraint is purely negative: it is that it should be left to the empirical sciences to fill in the details about which perfectly natural monadic properties there are (at least, in actuality: philosophy might teach us, or at least give us some reason to believe, that there are, in other possible worlds, so-called “alien” properties, perfectly natural properties not instantiated in the actual world). Not just any empirical science will do: given, in particular, the first of the four theses, it is really the job of fundamental physics to fill in these details. The special sciences get no say.