David Policar 1997
In a recent conversation with another friend of mine interested in linguistics and cognition, the phrase "Colorless green ideas sleep furiously" came up. For the uninitiated, this is a classic -- one might even say clichéd -- example of a sentence that follows the rules of English syntax and uses normal English words in ways that do not violate any formal rules of English usage, and yet fail some crucial test that native speakers of English consistently and effortlessly apply... the sentence doesn't mean anything. In fact, it's an intentionally and egregiously meaningless sentence, hence its popularity. I believe it was first coined by Noam Chomsky, though I could be wrong. Nevertheless, I'll be referring to it as the Chomsky sentence hereafter.
Anyway, we got to thinking about just what it was that made it meaningless. Basically, the Chomsky sentence is the opposite of an Escher print: in an Escher print, a series of locally reasonable-looking scenes are combined "illegally" to make an impossible whole, whereas in the Chomsky sentence, a series of locally impossible phrases are combined "legally" into a formally coherent whole. Things can certainly sleep, and actions can be performed furiously, but "colorless green" is a contradiction, and "sleep furiously" has difficulties associated with it, and assigning either phrase to "idea" does serious violence to our idea of what ideas are, what properties they have, and what they can do. And this is all pretty self-evident to any native English speaker.
I recommend, before reading further, that you assure yourself that the Chomsky sentence really is meaningless... the remainder of this monologue will be less entertaining otherwise.
So I forget why, but we got to thinking about what it might *possibly* mean.
Well, the word "green" can mean "inexperienced." We talk about a "green soldier" or a "green technician" by which we mean an inexperienced one, one that is not ripe. We certainly don't understand the adjective to imply color, when used in this sense. And so, by the same token, a "green idea" would be a new idea, one that has not been thought through clearly. It's an unusual construction, and clearly a metaphorical one, but perfectly reasonable. In fact, it's far more reasonable than the more common "half-baked idea," which raises nary an eyebrow, or the clearly ridiculous "mauve idea."
Now, it seems unambiguous that an idea can be said to sleep. At the very least, ideas are commonly said to lie dormant, and the use of "sleep" as a general term referring to a state of dormancy is common. Seeds in wintertime are often said to be sleeping; one may be accused of anthropomorphism in saying so, but not of incoherence. So "ideas sleep" is meaningful in the same way. For example, "The idea of democracy slept undisturbed for many years until awoken by the events of the American Revolution." It's perfectly clear what that sentence means.
Thus, we have a proto-Chomsky sentence: "Green ideas sleep." Not only is this not contradictory, it's practically tautological -- after all, if an idea isn't sleeping, then it has probably been thought about a reasonable amount, and can't properly be said to be green. That green ideas sleep is largely intrinsic to the definition of a green idea.
Of course, we all know -- well, most of know, or at any rate believe -- that ideas don't have colors. An idea can be of a color, or of something colorful, but that's an entirely different proposition -- the idea itself is not visible, and therefore can't have a color. So all ideas, green or clichéd, are colorless; that's obvious and not typically worth mentioning. So if green ideas sleep, then colorless green ideas sleep. This is doubly tautological... at about this point, we begin to wonder whether there's anything new being said at all. On the other hand, the whole notion is sufficiently unusual that one can forgive the Chomsky sentence for emphasizing and re-emphasizing its basic thesis about green ideas. In any case, it seems uncontroversial by this point that "Colorless green ideas sleep." has a referent, although one might question whether the referent is worth thinking about.
One might argue here that ideas are objects, not subjects. An idea doesn't actually *do* anything, it just is. When we say an idea sleeps, we really mean to say that there isn't any thinking system currently thinking that idea, in the same way that when we say an idea spreads quickly, what we really mean is that a lot of thinking systems start thinking that idea all at once. I would agree wholeheartedly.
On the other hand, it's awkward and clumsy to phrase it that way, and we typically ascribe motivations and activities to inanimate objects in our language precisely to avoid that awkwardness. We say "That car hates me" to express, succinctly and evocatively, a series of interactions with the car in question, and nobody questions our sanity or understands us to be seriously professing a belief in animism. In the same way, then, we say that an idea propogates itself, or defends itself (as in "A belief in conspiracy theories is an idea well-equipped to defend itself -- anyone arguing against it is self-evidently part of the conspiracy!"), etc. Ascribing activity to an idea is not problematic, and characterizing the manner in which that activity is performed is no more so -- an idea can be said to spread energetically through a community, for example.
So the question is, what does it mean -- if anything -- to "sleep furiously"? Well, I don't know about you, but I've certainly had bouts of sleeping furiously -- when my bedmate insists on telling me long stories at two in the morning while I desperately try to avoid being fully awoken, for example. This is in precisely the sense that I'm often said to be working furiously, or writing furiously -- doing it, or attempting to do it, with great intensity and focus and urgency. Success is not guaranteed, or implied -- I can be working furiously while accomplishing nothing, and I can even be writing furiously without actually having a single sentence to show for it. So I empathize with the notion of sleeping furiously, and even feel somewhat sorry for any entity driven to it. It's a sad state.
So I can understand what it might be like for a colorless green idea to sleep furiously... in the metaphorical sense in which I would understand a colorless green idea to be replicating furiously. Sometimes, an idea just doesn't seem to want to be thought... a self-destructive meme, you might call it. For example, the notion common to many mystical traditions that the ego is an illusion and the self doesn't really exist is an idea that, by its nature, tends to stay asleep... in fact, will often continue to stay so despite many sincere attempts at awakening it. If that isn't sleeping furiously, I don't know what is... it sounds exactly like the way I behave at two in the morning when my alarm clock is set for seven.
I reiterate that I am not ascribing any kind of volition or emotion or awareness to the ideas themselves, merely adopting a common English shorthand of anthropomorphizing inanimate objects -- in this case, ideas.
So, the Chomsky sentence seems meaningful after all... it is an admittedly poetic way of asserting that ideas which have not been well thought-out tend not to be thought about much, even when strong attempts are made by thinking systems to think them.
By the way, having determined what the sentence means, one might be tempted to wonder whether it's true or not. Which is also somewhat interesting. Let's consider a particularly intriguing example: the one referred to by the Chomsky sentence itself. It is certainly colorless, and I think it can be said with justice to be green -- certainly, I've never heard the sentence interpreted this way before, and I don't think it's been well thought out. And my experience in first coming up with the interpretation was that it strongly resisted being thought... again, an admittedly anthropomorphic way of expressing a complex, ill-defined state of mind I was in at the time, but a useful shorthand nevertheless. So this particular colorless green idea slept furiously, although ultimately unsuccessfully. Nevertheless, the sentence "This colorless green idea slept furiously." is true enough, in my experience. You may disagree.
You might also want to think about the following variant on the Chomsky sentence: "This colorless green idea sleeps successfully." As near as I can figure out, it is an intriguing variation on the Epiminedes paradox -- it is a sentence that is false if meaningful, but meaningless if true.