The paper argues that Lewis' Genuine Modal Realism, in taking the plurality of worlds to be necessarily the way it is, implies the existence of necessary connections of the sort that contradicts the Humean thesis that Lewis endorses. By endorsing, pace Divers, a non-redundancy interpretation of advanced modalizing, we gain the means to exactly state what these connections amount to.

According to Essentialism, an object’s properties divide into those that are essential and those that are accidental. While being human is commonly thought to be essential to Socrates, being a philosopher plausibly is not. We can motivate the distinction by appealing—as we just did—to examples. However, it is not obvious how best to characterize the notion of essential property, nor is it easy to give conclusive arguments for the essentiality of a given property. In this paper, I elaborate on these issues and explore the way in which essential properties behave in relation to other related properties, like sufficient-for-existence properties and individual essences.

Disclaimer: I say here that “if Sortal Essentialism is false, then surely Necessity of Origin is false as well” (268). For instance, if Socrates could be a dog—Sortal Essentialism being thereby false—then Socrates could have origins different from his actual ones. Such a claim, however, assumes two theses, one of which Mackie is sympathetic to, but the other one of which Mackie would most likely deny. My assuming them is therefore dialectically objectionable. The thesis Mackie is sympathetic to is the thesis that fundamental kinds obey the principle “once an F, always an F” (see chapter 7). The one Mackie would most likely deny, is a thesis according to which there are individuative conditions for origins such that, if x is a human-origin in one world, then x cannot be a dog-origin in another world. I have elaborated more on this here.

Due to the influence of Nathan Salmon’s views, endorsement of the “flexibility of origins” thesis is often thought to carry a commitment to the denial of S4. This paper rejects the existence of this commitment and examines how Peacocke’s theory of the modal may accommodate flexibility of origins without denying S4. One of the essential features of Peacocke’s account is the identification of the Principles of Possibility, which include the Modal Extension Principle (MEP), and a set of Constitutive Principles. Regarding their modal status, Peacocke argues for the necessity of MEP, but leaves open the possibility that some of the Constitutive Principles be only contingently true. Here, I show that the contingency of the Constitutive Principles is inconsistent with the recursivity of MEP, and this makes the account validate S4. It is also shown that, compatibly with the necessity of the Constitutive Principles, the account can still accommodate intuitions about flexibility of origins. However, the account we end up with once those intuitions are consistently accommodated may not be satisfactory, and this opens up the debate about whether or not artefacts allow for some variation in their origins.

In ‘A New Route to the Necessity of Origin’, Rohbaugh and deRosset offer an argument for the Necessity of Origin appealing neither to Sufficiency of Origin nor to a branching-times model of necessity. What is doing the crucial work in their argument is instead the thesis they name ‘Locality of Prevention’. In this response, we object that their argument is question-begging by showing, first, that the locality of prevention thesis is not strong enough to satisfactorily derive from it the intended conclusion, and, second, that the argument is not sound unless the Necessity of Origin is operating as an implicit premise.