Existence is often 'invisible' to analytic types well-versed in logic, for existence is "odious to the logician" as George Santayana sagely remarked in Scepticism and Animal Faith (Dover, 1955, p. 48) It is so odious, in fact, that they need to mask it under the misnamed 'existential' quantifier. So I need to resort to extreme methods to bring it into view I will quote from Jean-Paul Sartre's Nausea.
Now it goes without saying that I don't agree with Sartre that existence is an unintelligible surd. For me it is the opposite of unintelligible. But what I will borrow from Sartre is the insight that existence is extralogical: it is precisely not what Quine said it was whn he said that "Existence is what existential quantification expresses." So let's consider the famous 'chestnut tree' passage.
Roquentin, the protagonist, is in a park when he has a bout of temporary aphasia while contemplating the roots of a chestnut true. Words and their meanings vanish. He finds himself confronting a black knotty mass that frightens him. Then he has a vision:
It left me breathless. Never, until these last days, had I understood the meaning of 'existence.' I was like all the others, like the ones walking along the seashore, all dressed in their spring finery. I said, like them, 'The ocean is green; that white speck up there is a seagull,' but I didn't feel that it existed or that the seagull was an 'existing seagull'; usually existence hides itself. It is there, around us, in us, it is us, you can't say two words without mentioning it, but you can never touch it. When I believed I was thinking about it, I must [have] believe[d] that I was thinking nothing, my head was empty, or there was just one word in my head, the word 'to be.' Or else I was thinking . . . how can I explain it? I was thinking of belonging, I was telling myself that the sea belonged to the class of green objects, or that that green was a part of the quality of the sea. Even when I looked at things I was miles from dreaming that they existed; they looked like scenery to me. I picked them up in my hands, they served me as tools, I foresaw their resistance. But that all happened on the surface.
If anyone had asked me what existence was, I would have answered, in good faith, that it was nothing, simply an empty form that was added to external things without changing anything in their nature. And then all of a sudden, there it was, clear as day: existence had suddenly unveiled itself. It had lost the harmless look of an abstract category: it was the very paste of things, this root was kneaded into existence. Or rather the root, the park gates, the bench, the sparse grass, all that had vanished: the diversity of things, their individuality, were only an appearance, a veneer. This veneer had melted, leaving soft, monstrous masses, all in disorder — naked, in a frightful, obscene nakedness. (p. 127 tr. Lloyd Alexander)
This marvellous passage records Roquentin's intuition (direct perception) of Being or existence. (We will have to compare in a subsequent post Jacques Maritain's Thomist intuition of Being with Sartre's existentialist intuition of Being.) Viewed through the lenses of logic, 'The green sea exists' is equivalent to 'The sea is green' and 'The sea belongs to the class of green objects.' For the logician, then, 'exists' and cognates is dispensable and the concept of existence is fully expressible in terms of standard logical machinery.
But as I have been arguing ad nauseam (so to speak) over many a blog post, published articles and book, sentences like 'The sea is green' presuppose for their truth that the sea is an existing sea. Compare the reference above to an existing seagull. And, as Sartre has Roquentin says, "usually existence hides itself." It hides itself from all of us most of the time when we are immersed in what Heidegger calls average everydayness (alltaegliche Durchschnittlichkeit, vide Sein und Zeit), and existence hides itself from the logician qua logican all the time. For all of us most of the time, and for logicians all of the time, "existence is nothing, simply an empty form."
What the logician does is to substitute logical Being for real Being. Note that I am not endorsing Sartre's theory of real Being: that it is an absurd excrescence, de trop (superfluous), unintelligible, etc. What I am endorsing is his insight that real Being is extralogical, that it is not a thin notion exhausted by the machinery of logic.
But what if you are one of those sober types who has never experienced anything like Heideggerian Angst or Sartrean nausea or Wittgenstein's wonder at the existence of the world? Well, I think one could still be brought by purely discursive methods to understand how existence cannot reduce to a purely logical notion. We shall see.