I just ran a search of this forum and after more than ten years of activity I don't see a single mention of the phrase "castles in the air." It is highly irritating to me that the first use of this very appropriate characterization of anti-Epicurean philosophies has to come from ClaudeAI. However - I'll take it. Now that I think about it I haven't heard the phrase used much at all in many years . Here's the resurrected application, followed by Don McLean (who might be responsible for my remembering it at all). I feel sure that there are at least a couple of others who will remember the same reference.
The Common Thread in All Cases of Epicurus vs Idealism
What is striking is how consistently the same Epicurean moves apply:
Every form of modern idealism, in different ways, interposes something between the knower and the world — divine mind, cognitive apparatus, Absolute Spirit, irreducible qualia. In every case Epicurus would say: the Canon does not attest to this interposition, and each of these additions generates more problems than it solves while delivering less than Epicurean materialism already provides cleanly.
The deeper issue is that modern idealism, like its ancient predecessors, typically begins with a puzzle (how do we have certain knowledge? what is consciousness? how can contingent things exist?) and then constructs a metaphysical architecture to solve it. Epicurus's method runs in the opposite direction: start with what the Canon delivers and build only as far as the evidence warrants. Any architecture built higher than that foundation is, regardless of its internal elegance, a castle in the air.