Inspired by this thread: Does a canal cutting across an isthmus make an island?
Are there any such things as definitions or categories of things that could exist, but that now contain no remaining examples/members, where all of the initially included members have been nitpicked or redefined out somewhere else? - Not by refinement of the definition, but by simple examination of the facts about the members.
Democracy.
Communism.
Heck, every “ism” ever.
I’m afraid I don’t quite follow what the OP is asking for. An abstract category with no members? I think mathematicians allow that logically, don’t they?
You create category x with a specific definition, containing various examples. On closer examination (and without changing the definition) you discover that none of the original items (and no additional items) fit the definition.
For example, if you defined planets as being perfect spheres, then you measured all known planets and see those none of them are perfect spheres, then there would be no known planets.
This is one of those concepts that I know exists but can’t think of a more general example of.
In terms of hobbyist opinions, I remember back when it was the current system in the 90s people often pointed out the Nintendo N64 console had no Role-playing-games, which was seen as a massive detriment since Nintendos previous systems were home to plenty of RPG style games. Nintendo fans countered that the N64 DID have a few RPGs, notably both Legend of Zelda games, Quest 64, and Ogre Battle 64.
However since those arguments all of those games are no longer considered RPGs since the definitions have changed due to more games coming out since then. Now it’s generally agreed Legend of Zelda is an Action-Adventure game, Quest 64 is also an action adventure game with ROG elements, and Ogre Battle 64 is a tactics and strategy game.
However there is a single example of an actual RPG on the system, Paper Mario. Though detractors may claim it’s not a “true” RPG but a highly simplified one.
Would parallel universes count? One definition of “the universe” is “the totality of everything that exists”, so by that definition, a plane of being similar but divergent from the one we know of would still be part of the universe.
I see what you mean, but parallel universes are hypothetical - I did think about magnetic monopoles as a possible example, but the question here is more about looking for an orphaned category that formerly contained members, but is now empty.
This is the kind of thing I was looking for - basically non-fallacious cases of No True Scotsman
Maybe it’s useful to distinguish between extension and intension, here—so, the extension of a concept is essentially all of the things that fall under it, while the intension defines necessary and sufficient conditions for things to fall under that concept. So, it used to be held that the extension of ‘knowledge’ was equivalent to the intension of ‘justified true belief’ (JTB), before Gettier pointed out that there were items of knowledge that aren’t JTB. If I understand the OP right, then we’re looking for concepts with empty intensions.
For one example, take the concept of ‘boring number’, i. e. a number about which there’s nothing special. If there is such a thing, then there’s a least (i. e. smallest) boring number. Then, that number isn’t boring, it’s special; so, it must be removed from the set of boring numbers. But then, there’s a new least boring number, and so on, until one finds the set of boring numbers to be empty.
But of course, that’s somewhat cheating. I feel like there’s some example from biology I’m barely remembering, some clade that was found to actually be empty, or something. Then there’s of course huge swaths of alleged paranormal phenomena, encounters with aliens, etc.—every single one has, upon closer inspection, been found not to actually be an example of what it was supposed to be.
I feel like I’m proposing things that, upon closer inspection, don’t actually fall under the OP’s topic. So perhaps, the concept of ‘things where all of the potential examples have been nitpicked to be outside of the definition’ is such a thing—but then, of course, it isn’t! Which means it is…
Yeah, I don’t see why mythical things should be excluded - all that is needed to qualify for this thread is that there was a group that people substantially considered to be full of things, and that those things eventually all ended up outside of that group. Perhaps these things are a bit of a special case in that they got outside of the group by virtue of being found to not actually exist, but I’m not going to disqualify on that basis.
Yes, there’s a scale effect.
I’ve always quibbled with the description of outer space as a ‘hard vacuum’. It isn’t; it has all those dirty great rocks in it.
I can’t off the top of my head think of any examples but I’m pretty sure I’ve heard of instances of this in the classification system for flora and fauna - where plants or animals have been put in a particular category but on close examination it’s been found that every instance actually belongs in a different category.
Rosemary being one of the latest examples of this. I recently discovered that Rosemary - which used to be a genus of its own - Rosamarinus - is now just included in the genus Salvia.
But this is a case of a category becoming defunct rather than empty - nobody is out there looking for examples that might now fit into the genus, which is subtly different from a category of items that theoretically could exist, with no known examples to fill it
My advisor used to say “We absolutely know that magnetic monopoles exist. There just might be a very small number of them, such as zero.” In other words, we know that under the right conditions, they would exist, but those conditions may well be rare enough that they would never actually occur anywhere in the observable Universe.