- Professor Plantinga's careful and penetrating comments2 have thrown considerable light upon the difficult philosophical questions that are involved in the thesis of mereological essentialism.
- I will comment upon five points.
- In the paper Plantinga refers to3, I had set forth three axioms for what I had called the strict and philosophical sense of the term "part," or "proper part." These axioms tell us, in effect, that the expression "x is an S-part of y" ("x is a strict proper part of y") expresses a relation that is transitive, asymmetric, and such that x bears it to y at all times that y exists.
- In weighing philosophical views, it is important to consider them in relation to their alternatives, if they have alternatives. My view, which is appropriately called "extreme mereological essentialism," may be put this way:
- For every x and y, if x is ever part of y, then y is necessarily such that x is part of y at any time that y exists.
I had contrasted this view with "extreme mereological inessentialism":
- There is no x and no y such that y is necessarily such that it ever has x as a part.
I had suggested in my paper that extreme mereological inessentialism is absurd.
- Given my way of looking at these things, it is, as Plantinga notes, a very easy step to the view that the objects of common sense – the vulgar objects, as I had called them – are fictions.
- Plantinga introduces the expression, "the Principle of Mereological Changelessness," as a name for the following principle which I had set forth at the outset of my paper: "If y is ever a part of x, then y is a part of x at any time that x exists." I would point out that this name is somewhat misleading (though Plantinga himself is not misled by it). The view that I have advocated is not like that of Parmenides.
- Finally, I take this opportunity to correct one defect of the original system by adding a clause to the definition I had proposed of "x is discrete from y".
Footnote 2: Footnote 3:
- The “Five Points” are taken from the Introductions to the corresponding Sections.
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