One can, arguably, imagine that a brick pops into existence uncaused. Therefore, one might conclude that it is possible that a brick pops into existence uncaused, and hence that the PSR is not a necessary truth. This is a popular Humean argument against the PSR.
The defender of the PSR can, of course, simply insist that the inference from imaginabil-ity to possibility is defeasible. After all, someone might imagine that a certain straightedge and compass construction trisects an angle,9 and if the inference from imaginability to possibility were indefeasible, it would follow that the construction possibly trisects an angle. But a mathematical construction possibly (in the metaphysical sense) trisects an angle if and only if it actually does so, and in fact we know that angles cannot be trisected with straightedge and compass. So the inference had better be defeasible. The defender of the PSR can then claim that the arguments for the PSR are so strong that the argument from imaginability of PSR failure, being defeasible, does little to shake our confidence in the PSR.
However, there is a better solution for the defender of the PSR, and this is to question the claim that the opponent has actually imagined a brick popping into existence uncaused. It is one thing to imagine something without simultaneously imagining its cause, and another to imagine something along with the absence of a cause. In fact, the task of imagining absences as such is a difficult one. If I tell an ordinary person to imagine a completely empty room, the subject is likely to imagine an ordinary room, with walls but no furniture. But has the subject really imagined an empty room? Likely not. Most likely the imagined room is conceptualized in a way that implies that it has air in it. For instance, we could ask our subject what it would be like to sit in that empty room for 8 hours, and our subject is unlikely to respond: "You'd be dead since the room has nothing in it, and hence no oxygen either."
Could one with more directed effort imagine a room without any air in it? I am not at all sure of that. While we have the concept of vacuum as the absence of anything, it is not at all clear that we can imagine vacuum. Our language may itself be a giveaway of what we imagine when we imagine, as we say, a room "filled" with vacuum - perhaps we are not really imagining an empty room, but one filled with some colorless, frictionless, zero-pressure substance. Moreover, most likely, we are imagining the room as embedded in a universe like ours. But a room in a universe like ours will be pervaded with quantum
9. In fact, many people have imagined just that (see Dudley 1987).
vacuum as well as with electromagnetic and other fields, and perhaps even with spatial or spatiotemporal points. Whether these "items" count as things or not is controversial, of course, but at least it is far from clear that we have really imagined a truly empty room.
It is true that philosophers sometimes claim that they can imagine a world that, say, consists only of two iron balls (Black 1952). But a claim to imagine that is surely open to question. First of all, the typical sighted person's imagination is visual. The balls are, almost surely, imagined visible. But if so, then it is an implicit part of what one is imagining that there are photons bouncing off the balls. Furthermore, unless one takes care to specify -and I do not know how one exactly one specifies this in the imagination - that the balls obey laws very different from those of our world, there will constantly be occasional atoms coming off the edges of the balls, and hence there will be a highly diffuse gas around the balls. Suppose all of this physics is taken care of by our careful imaginer. Still, have we really imagined a world containing only two balls? What about the proper parts of the billiard balls - does the world not contain those? What about properties such as roundness, or at least tropes such as this ball's roundness? And are there no, perhaps, spatial or other relations between the balls? We see that unless one is a most determined nominalist, the content of the imagined world is going to be rather richer than we initially said. There are details implicit in the imagined situation that we have omitted.
There may, however, be a way we can imagine an absence. We can probably imagine absences of particular kinds of things in a particular area of space-time. Certainly, I can imagine a room free of talking donkeys, or even of donkeys in general. Moreover, I can probably imagine a room with no particles or electromagnetic fields in it. But that is not the same as imagining a truly empty room. A truly empty room does not have any other kinds of fields in it, at least if fields are things; there are no points of space or space-time in it; and it certainly has no ghosts, angels, or demons in it. But no list of kinds of things that we imagine as absent from the room will assure us of the literal and complete emptiness of the room, for there may always be a different kind of being, one utterly beyond the powers of our imagination, whose absence from the room we have failed to imagine. Nor will it do to imagine "unimaginables" as missing since "unimaginables" are not a genuine kind of thing but, surely, a mix of very different kinds of possibilia -it seems highly plausible that there are many kinds of possible things beyond our wildest imagination.
Similarly, we can imagine a brick coming into existence in the absence of a brickmaker, a brick not resulting from the baking of clay, a brick not made by an angel, demon, or ghost. But that is not the same thing as imagining a brick that comes into existence completely causelessly. To imagine that, we would need to imagine every possible kind of cause - including the unimaginable ones - as absent. That seems to be a feat beyond our abilities. We can, of course, say the words "This is causeless" both with our lips and with our minds while imagining the brick, but the claim that whenever one can imagine an F and say of it, with lips or minds, that it is a G, then, possibly, there is an F that is a G, would not only be highly defeasible but would also surely be a nonstarter. I can imagine a circle and say the words "This is a square" while imagining it.
Moreover, in general, when we imagine a situation, we imagine not a whole possible world, but a part of one, and our imagination is neutral on whether there are further support structures. I imagine three billiard balls on a billiard table. Probably, it is part of my imagining that there is gravity. Something, then, has to hold the table up, but what it is is not a part of the imagined situation. But I am not imagining a table miraculously suspended in a gravitational field - I am simply not imagining what the outside of the situation has to be like to support the part I care about.
Maybe, with a lot of work, one can imagine a situation involving a brick and involving enough imagined detail that one can, with confidence, say that the situation is not only one where the ordinary causes of bricks are not present near the brick, but where nowhere in the universe are there any causes of the brick and where there are no nonphysical causes of the brick either. But now we see that the situation imagined took rather more effort, and the given examples of how there may be more to an imagined situation than one initially thought should severely reduce one's confidence that one has been successful at the task of imagining a causeless brick. And even if one has been successful at it, the inference to the possibility of a causeless brick is still defeasible.
I want to end this discussion by comparing the imaginability argument for a causeless brick with the imaginability argument against Platonism. One might claim that it is possible to imagine a brick that does not stand in an instantiation relation to any other entities. If one can, then defeasibly it follows that possibly a brick does not stand in an instantiation relation to any other entities. But that, of course, contradicts Platonism, which holds that, necessarily, all bricks instantiate brickness. While I am not a Platonist, this argument against Platonism strikes me as weak. The Platonist can answer as I did earlier: have we really imagined a brick that does not stand in an instantiation relation to another entity, or have we merely imagined a brick without imagining its standing in an instantiation relation?
But there is also a further answer the Platonist can make. The Platonist can say: "For all you know, by imagining it as a brick you have implicitly imagined a situation where it is related to brickness, although your description of the contents of what you imagined contradicts this." Compare this to the point one should make against someone who claims that to have imagined a cube without any space or spatial relations - surely, by imagining it as a cube, you have implicitly imagined it as occupying space or as involving spatial relations (say, between the vertices).
Can the defender of the PSR make this point too? Perhaps. The brick we allegedly imagine coming into existence ex nihilo is a contingent brick. But it might be that the nature of contingency involves being caused (cf. Section 184.108.40.206, above). Moreover, the brick has existence. But it seems implausible to claim that we have plumbed the depths of the nature of existence. It could, for instance, be that to be is either to be necessary or to be caused -that the esse, the existence, of a contingent being is its being caused (it may be that Thomas Aquinas thought this; I explore this kind of a view in Pruss 2006, chap. 12). It could even be that the esse of a contingent being is its being caused by that particular set of causes by which it is caused - that would cohere neatly with and explain the essentiality of origins.
A variant of the argument from modal imagination is to say that one can without overt logical contradiction state the claim that a brick exists without a cause:
However, that is a bad argument. That one can state something without overt contradiction does not imply that there is no hidden contradiction. After all, compare (9) with:
This claim is impossible since it is a necessary truth that sculptures have sculptors - that is what makes them be sculptures. In the case of (10) the contradiction lies pretty close to the surface. But how do we know that in (9), there is no contradiction somewhat further from the surface? Maybe there is even a hidden complexity in the concept represented by the existential quantifier.
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