As usual, this is a philosophical "problem" caused by overanalysis of language. A cloud exists when someone can say "that's a cloud" and a listener thinks "yes, that is a cloud", or that fact is somehow meaningful to them in their life.<p>If you're a pilot, a cloud is a way to talk about something that reduces your visibility and causes turbulence. If you aren't carrying an umbrella, a cloud may be a sign you're about to get wet. The fact that these phenomena share the name "cloud" is only meaningful to the extent that they arise from the same sort of physical processes. But trying to rigidly assign a particular arrangement of physical processes to a single entity "cloud" leads to the nonsense you see here.<p>Nobody using the word "cloud" cares about this assignment. They care about whether there'll be turbulence, or whether they're likely to get wet, or whether the cloud looks like a bunny rabbit or whatever. The solution to the paradox is to realize that not all concepts are analyzable to this degree, and that that's OK.
The lack of inherent existence of the cloud seems to be the most logical solution to this problem. Although the cloud has no inherent existence, if we look at the same spot in the sky, I have a perception of a cloud, and you have a perception of a cloud. Our perceptions are not the same, and when we get to the edges of the cloud the boundaries we perceive are highly likely to differ. Nevertheless, because our perceptions have so much in common, I can say "that cloud" to you will know what I am talking about. Your perception will still differ from mine, especially along the borders of the cloud, but the differences in perception are not likely to be important for the sake of our discussion. The author's rebuttal in paragraph 3 of the Nihilism section looks weak to me.
Seems useful to think of this from a computer vision standpoint. With vision problems, you often first need human annotation, and unless human beings can agree to a high degree, there are going to be problems. The "number of clouds" in a picture is an ambiguous enough concept that I can't imagine everybody agreeing.<p>That said, if there is clearly _one_ cloud, I think most annotators would agree that there is one cloud (and not, say, infinitely many).<p>So going from that, you can frame it as a constraint optimization problem. You want the largest possible collection of droplets to be a cloud, without accidentally defining all the clouds in the world into a single cloud. There has to be a loss function for the cloud-ness of a set of droplets based off how dispersed the droplets are in it.<p>Think about the fill bucket in Microsoft Paint. A single pixel hole allows the entire image to get painted one color. We don't want our definition of cloud to leak along the single droplets that exist in the air to define the entire atmosphere as a cloud, but we definitely want to group certain things together as clouds.<p>Hopefully that is food for thought for someone who is better versed at the specifics of anything I just said!
Reminds me of a strange story by Philip K. Dick titled "Null-O". The protagonists of that story are complete (and militant) mereological nihilists.
A physicist's point of view:<p>P.W. Anderson, "More is Different" (1972), <a href="http://robotics.cs.tamu.edu/dshell/cs689/papers/anderson72more_is_different.pdf" rel="nofollow">http://robotics.cs.tamu.edu/dshell/cs689/papers/anderson72mo...</a><p>(One of my favourite essays on philosophy of science, by scientists. Perhaps just after Wigner's "The Unreasonable Effectiveness of Mathematics in the Natural Sciences".)
>It would be profoundly counterintuitive if there were no clouds, or no cathodes, or no humans, and that is probably enough to reject the position<p>I really hate it when philosophers make "arguments by intuition". It's almost always used to justify denying some aspect of reality, or even worse, some ethical tradition.
Maybe there is a difference between an idea and a concept. I have an idea of a cloud. I have no strong concept of a cloud, and that would not matter unless faced with a problem that required a strong concept of a cloud in order to resolve the problem.<p>Is there a problem? Seems to me if there were an actual and important problem whose solution were dependent on "what a cloud is" then you would have no shortage of conceptualizations. What then matters is to what extent they are useful for resolving problems.<p>I believe this is quite normal and our conceptualizations of ideas change as the problems we face change. For instance, you can always ask what does Justice, the Idea, mean. People have developed concepts over time and applied them. The success leads to further problems, asking again what Justice means, and further concepts.
The universe is (most likely..) made of atoms, protons electrons etc. On the other hand is seeing is done by the seer.. So we define where stuff begins and ends, and if we disagree about it, well, that's just fine.
A single cloud in the sky may exist in such fashion that it has no precise boundary and is not constituted by any specific set of water droplets. We invented the word cloud as a name for loosely grouped water droplets that appear white and fluffy when viewed from a far (as they commonly are). No "contradiction" here.