Two commenters in an earlier van Inwagen thread, the illustrious William the Nominalist and the noble Philoponus of Terravita, have raised Moore-style objections to an implication of PvI's claim that "every physical thing is either a living organism or a simple" (MB 98), namely, the implication that "there are no tables or chairs or any other visible objects except living organisms." (MB 1) The claim that there are no inanimate objects, no tables, chairs, ships and stars will strike many as so patently absurd as to be not worth discussing. Arguments to such a conclusion, no matter how clever, will be dismissed as unsound without evaluation on the simple ground that the conclusion to which they lead is preposterous. This is the essence of a Moorean objection. If someone says that time is unreal, you say, 'I ate breakfast an hour ago.' If someone denies the external world, you hold up your hands. If someone denies that there are chairs, you point out that he is sitting on one. And then you clinch your little speech by adding, 'The points I have just made are more worthy of credence than any premises you can marshall in support of their negations.'
I myself have never been impressed with Moorean rebuttals. To my mind they signal on the part of those who make them a failure to understand the nature of philosophical (in particular, metaphysical) claims. See, e.g., Can One See that One is not a Brain in a Vat?
Though I disagree with van Inwagen's denial of artifacts, I think he can be quite easily defended against the charge of maintaining something 'mad' or something refutable by a facile Moorean rejoinder.
Chapter 10 of Material Beings deals with the Moorean objection. Van Inwagen does not deny that we utter such true sentences as 'There is a wall that separates my property from my neighbor's.' But whereas most of us would infer from this that walls exist, and thus that composite non-living things exist, van Inwagen refuses to draw this inference maintaining instead that the truth of 'There is a wall that separates my property from my neighbor's' is consistent with there being no walls.
This is not as crazy as it sounds. For suppose that what the vulgar call a wall is (speaking with the learned) just some stacked stones, some stones arranged wall-wise. And to simplify the discussion, suppose the stones are simples. Then the denial that there is a wall is a denial that there is one single thing that the stones compose. But this is consistent with the existence of the stones. Accordingly, the sentence 'There is a wall that separates my property from my neighbor's' is true in virtue of the existence of the stones despite the fact that there is no wall as a whole composed of these stony parts.
Or consider the house built by the Wise Pig years ago out of 10, 000 blocks (which for present purposes we may consider to be honorary simples.) (The tail tale of the Wise Pig is recounted on p. 130 of Material Beings.) At the completion of construction, did something new come into existence? I would say 'yes.' Van Inwagen would say 'no.' All that has happened on PvI's account is that some blocks have been arranged house-wise. His denial then, is that there is a y such that the xs compose y. He is not denying the xs (the blocks construed as simples); he is denying that there is a whole that they compose. And because there is no whole that they compose, the house does not exist.
Furthermore, because the house does not exist, there can be no question whether the house built by the Wise Pig years ago, and kept in good repair by him and his descendants by replacement of defective blocks, is the same as or is not the same as the one that his descendants live in today. The standard puzzles about diachronic artifact identity lapse if there are no artifacts.
Does this fly in the face of Moorean common sense? If madman Mel were to say that there are no houses he would not mean what the metaphysican means when he says that there are no houses. If Mel is right, then it cannot be true that I have been living in the same house for the last ten years. But the truth of 'I have been living in the same house for the last ten years' is consistent with, or at least not obviously inconsistent with, PvI's denial of houses (which is of course not a special denial, but a consequence of his denial of artifacts in general). This is because PvI is not denying the existence of the simples which we mistakenly construe as parts of a nonexistent whole.
But then how are we to understand a sentence like, 'The very same house that stands here now has stood here for three hundred years'? Van Inwagen proposes the following paraphrase:
There are bricks (or, more generally, objects) arranged housewise here now, and these bricks are the current objects of a history of maintenance that began three hundred years ago; and at no time in that period were the then-current objects of that history arranged housewise anywhere but here. (133)
I am not endorsing PvI's denial of artifacts, I am merely pointing out that it cannot be dismissed Moore-style.