On page 11 of this article by Timothy Williamson http://link.springer.com/article/10.1007/s10670-013-9474-z#page-12
the Barcan schema in first-order modal logic is discussed. Williamson says, "Informally, it says that if there could have been something that met a certain condition, then there is something that could have met that condition."
Would it not be better to modify Williamson's sentence as follows: Informally, it says that if there could be something that met a certain condition, then there is something that could meet that condition."
As a person interested in the semantics of natural languages I object to the treatment of the modally very different constructions "could be" and "could have been"; yes, both refer to possibilities, but of different kinds. So what is Timothy Williamson's motivation for conflating these distinct types of modal meaning?
The point does not concern how natural use of "could" is in this context but rather the question of why (and whether), in this particular context, should the modal operator in English be understood as what is often called the past conditional (could have), instead of the present conditional (could). This is not a question about naturalness; rather, it is a question about the evident difference in meaning between the two constructions. If I say "a war could start" this obviously has a very different meaning from "a war could have started".
