Why wouldn’t it be possible? In a second’s thought you could come up with examples of things that you know don’t exist; how would you denying they exist affect the fact of their non-existence in any way? I simply don’t see where your uncertainty comes from.
I wonder if this is related to the thing about not being able to prove (certain categories of) negative assertions. It sounds like it might be.
Certain things I have not (at least yet) thought of do not exist. In fact, certain things I cannot imagine do not exist.
I have disbelieved them without presupposing their existence. That, is, beyond the definition that a) they dont exist, and B) I cant imagine them.
Whatever life that gives them is very slim indeed.
sflgipubhl doesn’t exist.
And yes, that was just random typing above – I didn’t even have to think about the letter-sequence in positing something that doesn’t exist.
Yeah. “existence” or “non-existence” is not a property of the thing being described, though I suppose the existence or non-existence of something can be considered a property of the universe/reality if you can say that reality has properties.
I think that what I’m thinking about is actually a summary of Decarte, from an incomplete education. Granted, I haven’t read it in years, I seem to recall them making a point of ‘where did our idea of God come from’, and I extrapolated from there.
I have heard the argument (or rather, the confusion as you correctly note) on the web, in internet forums.
Concur. It only has properties if it exists. In order to deny its existence, it is not necessary to imagine all of the properties it possibly might have if it did exist, only to deny them.
Indeed some, many, most or all things - quite everyday things - may have properties we don’t even know about, and our knowledge or acknowledgment of these properties is unnecessary in the matter of our acceptance or denial of their existence.
You are not presupposing the existence of a thing, you are presupposing the hypothesis of the existence of a thing. Lacking any evidence you can deny it out of hand. In common speech though, we tend to be briefer and hop right to the point rather than going through all the steps.
“What if pink underwear goblins exist?” Is an example of the idea of something existing. Since there is no evidence of pink underwear goblins we can deny both the idea of them existing and the goblins themselves as one requires the other. It is simpler to state “Pink underwear goblins do not exist” though as the logical step is quite small and extremely nit-picky.
The biggest problem here is a lack of clear definition of the word “presuppose”, and by extension conflation of that term with the word “imagine”.
Just because I can imagine something does not mean I presuppose its existence. End of.
Further, there’s an inherent trick in the argument. To build on Frylock’s statement - if I tell you that a unicorn doesn’t exist, you would usually think of a unicorn, and deny its existence, because the imaginary being “unicorn” already exists in your mind. A proponent of this argument would indicate that - haha - you have presupposed unicorns. (This is, of course, untrue, you have only imagined them.)
However, if I tell you that Habalabafabanos don’t exist, you neither imagine them nor presuppose them, because you don’t know what they are. Yet you would be correct in concluding that they don’t exist.
The question reminds me, as it has others in this thread, of the ontological argument for the existence of God, which is the biggest crock of circular-reasoning horseshit I’ve ever heard.
There has to be something wrong with the Ontological Argument.
But it’s not at all easy figuring out what is wrong with it.
Well, Descartes (arguably) argued that since I can’t deny my own existence without, by engaging in that very mental act, affirming (if not exactly asserting) my own existence, I can be absolutely certain that I myself exist.
But that’s not supposed to generalize to other things. He didn’t rely on a general rule that asserting nonexistence presupposes existence. Rather, it was a specific observation just about his own experience of himself–that an attempt to mentally deny his own existence fails from the outset, since he has to exist in order to deny his own existence.
I think that the OP is asking whether the only way to argue for the nonexistence of something is to use a reductio ad absurdum line of argument on it. E.g:
Suppose A exists.
If A exists, then B, C, and D.
B, C, and D are ridiculous or obviously false, therefore…
A doesn’t exist.
But I think several posters have already shown that this isn’t the only way to argue against something existing. But it is a powerful and common method.
Sure, but you can also just say “goblins do not exist, in any form” and you’ve denied the existence of the pink underwear type, plus any number of other types, without forming any (detailed, at least) hypothesis about those.
I wanted to refer to **Der Trihs’ **example of Sauron, and then I noted that he changed the sentence from “doesn’t exist” to “isn’t real”. For the purpose of my argument, read that quote as:
‘Does saying “Sauron doesn’t exist” mean that I actually think Sauron does exist?’
I believe that I did see this argument turn up somewhere in one of those interminable Libertarian/**Liberal **Ontological Proof threads. I suspect that might be where the OP is coming from. In this case, it depends on obfuscating the meaning of “exist.” There is a sense in which we can reasonably say that *Sauron *exists. Come on, we all know what **Der Trihs **meant when he referred to Sauron; *Sauron *is a Maia corrupted by Morgoth; *Sauron *is a character in a novel by JRR Tolkein. Since we all know what is meant, the tag *Sauron *must refer to something, and therefore that *something *can be said to exist.
*Exist *is one of those words that are used a lot but are difficult to define well.
Which brings up the same question Meinong was addressing–does a thing have to exist in order to have properties?
“Sauron ruled in Mordor during the 3rd Age” appears to a lot of people to be a true sentence. But if it’s true, then it must be that Sauron does in fact have the property of ruling in Mordor during the 3rd Age. And if he has that property, and if having properties entails existence, then it must be that Sauron exists.
However, there are a lot of other equally plausible positions available:
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The sentence “Sauron ruled in Mordor during the 3rd Age” isn’t true. People sometimes call it “true” but when they do so they’re engaging in a game of pretend. (Insert argument that a correct understanding of what goes into a game of pretend shows that the objects pretended don’t need to exist.)
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The sentence is “true in a fiction” which is not the same thing as “true in reality” although it is a kind of truth. Truth in fiction doesn’t entail real existence.
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The word “Sauron” is short for a description something like “an entity occupying a place in the third level of a heiarchy of angelic beings ruled by a God name Iluvatar, who blahdee blahdee blah… and who ruled in Mordor during the 3rd age.” Once you supply appropriate definitions for “mordor” and “3rd” age as well, you find out the sentence is true tautologically, which means its truth doesn’t entail the existence of an entity matching Sauron’s description after all. (Similarly, “Square circles are square” is tautologically true, yet its truth doesn’t entail the existence of a square circle.)
I’m sure there are several other views available but those are the ones that came to mind.
I can define a four-sided triangle, and list its properties, yet I can’t visualize it and it doesn’t really exist in my mind.
This may be too simplistic, but perhaps the OP is thinking of a proof by contradiction, which disproves the existence of something by assuming (though not really presupposing) it exists, and then showing that its existence leads to a contradiction in some way.
I believe Bertrand Russell said something almost identical.
Here’s a Wikipedia summary of the argument from the Gödel ontological proof page (there are several): “God, by definition, is that for which no greater can be conceived. God exists in the understanding. If God exists in the understanding, we could imagine Him to be greater by existing in reality. Therefore, God must exist.”
The problem is with the third sentence, which I’ve emphasized. My comprehensive logical proof of its errancy is as follows: it’s utter bullshit.
Yeah yeah Gödel was a genius and I’m not, but even geniuses can fuck up from time to time. 
Moreover, the argument only allows for the existence of a single god, but there are thousands, so it’s axiomatically incorrect before you even start.
There is no spoon.
Is the OP asking whether all arguments of non-existence are reductio ad absurdum arguments? If so, I would say that you don’t have to presuppose something exists; you can simply say that Occum’s Razor means that you can (at least provisionally) reject the existence of anything not supported by sufficient evidence. (Or is that reductio ad absurdum in the sense of “if it existed, evidence would be there”?)
ETA post #32
In order for them to either exist or not exist, they must be defined. It would not be reasonable for me to conclude either that Habalabafabanos exist or that they don’t exist since in the absence of a definition you don’t have a concept to consider the existence of.