 Perhaps a more powerful interpretation of Locke's arguments would be to see them as an empirical challenge to (rather than as a refutation of) the idea that nature comes pre-structured by substantial forms. In reference to borderline cases, Locke could be arguing that, without assuming that there are substantial forms, nature does not give us convincing evidence of such order. The semantic argument can be seen as a similar empirical challenge: there is no evidence that nature is narrowly constraining the creation of our nominal essences (we have broad latitude in their creation), but if there were substantial forms we should expect much less latitude. It is this challenge that seems to undergird Locke's third argument: even though nature provides us with the qualities we ultimately include in our nominal essences, it is up to us to determine what goes into each nominal essence, and there is no place for a substantial form to be involved in that process. Although this might be a stretch, even Locke's fourth criticism may still function as an empirical challenge. Perception is a highly contentious subject that seems beyond our ability to explain, even by appeal to the existence of substantial forms. So, without evidence that there are such forms, there is no reason to take nature to be the locus of generality. Whether these replies would be effective, or even whether these are what Locke had in mind, it is clear that Locke was convinced that substantial forms are not a viable component of natural philosophy.