 Before Plato started doing philosophy, he tried to open a sandwich shop, but just couldn't get the paperwork together. Apparently he had a real problem with forms. Is a hot dog a sandwich? Is a taco or a hero or a burrito or a pop tart a sandwich? Is this a game? Is this art? Are viruses alive? Despite what the internet might have you believe, humans have been engaging in flame wars about these sorts of questions for thousands of years. Aristotle himself noted that the Iliad couldn't be rightly called just an epic or just a tragedy, but the critics of his time still argued furiously with each other to classify it as one or the other. But all these admittedly silly arguments are actually dancing around a more abstract question of metaphysics, the analysis of the fundamental nature of the ideas we use to understand the universe, like what exists, what are objects, what are properties, that sort of stuff. As ridiculous as it sounds, taking a hard line on the hot dog sandwich question is actually a move that has heavy metaphysical ramifications related to an old and still sticky issue in philosophy called the problem of universals. This is what metaphysicians would call a particular, this specific sandwich. This sandwich exhibits several properties. It smells tasty, it's soft, it's to my right, it's delicious, and it's a sandwich. I can imagine particulars that lack certain properties, like a sandwich that isn't delicious, but it's pretty hard to imagine a particular with no properties at all, or a property without a particular object embodying or exhibiting it. The way that we talk and think about our world is to treat properties as though particulars share them, like these things are the same color. Those things are both to the left of me. These things are all sandwiches. It's almost like we're saying there's one thing, sandwichness, that appears in these particulars and doesn't appear in those ones. But what sort of a thing is sandwichness, or redness, or bigger than ness? What is the medium we're using to group these things together and call them sandwiches, and to call those things not sandwiches? By virtue of what exactly are certain particulars the same, or alike, or different? This question sort of underlies our entire understanding of the universe and everything in it, and like many things in philosophy, there are several answers which all lead to some very interesting places. Let's start with Platonism, or Realism. Platonists believe that sandwichness and redness, and to the left of ness, and all these other properties, or relations, actually exist more or less the way we talk about them. The particulars that seem similar to us are similar because there's some essence that they're really sharing. So when we say that certain objects are the same color, or the same type, or have the same relationship, there is something realized in those objects that makes those statements literally true. On the one hand, that's kind of useful because it provides a simple mechanism by which these particulars relate to each other. They're instantiating the same whatever, exactly the way that we say that they do. Sandwiches are sandwiches because they're exhibiting sandwichness, but properties, if they actually have some sort of existence of their own, are ridiculously weird. It doesn't make any sense to ask where roundness is, or when it came into being. Roundness could theoretically appear in an infinite number of places, or one place, or even nowhere without being lessened or diminished in any way. I could destroy every round particular in the cosmos, wait for a thousand years, and still be confident that if something became shaped like this, roundness and everything that entails would appear in it. Roundness can be everywhere, or nowhere, which is why metaphysicians call it a universal, and you might start to see what the problem of universals is. That sounds crazy. Every single characteristic we can imagine, redness, sandwichness, is actually an entity that exists outside of space and time? Come on. But the Platonist position that properties and classes and relations are calling out real things that actually exist, no matter how weird those things end up being, is sort of biting a philosophical bullet to allow resemblance between particulars to keep working more or less the way it usually does in our heads. Chasing other interpretations of what universals really are also leads to weird places. If you don't accept the existence of universals at face value the way a Platonist does, odds are you're some kind of nominalist. For nominalists you can talk about redness and sandwichness and whatever other universals you like, but only unique particulars really exist. You can call a Panini sandwich and a grilled cheese sandwich, but it's a mistake to imagine that there's anything really connecting the two. There are several different versions of nominalism, each holding a slightly different interpretation of how things can have properties without universals. For example, concept nominalists or conceptualists assert that the categories and properties we think we see in multiple places are actually just concepts, mental phenomena. Sandwichness exists in some sense, but only in our heads. A thing only requires sandwichness because a thinking entity has assigned the concept of sandwich to it. That gets rid of universals, but conceptualism has some uncomfortable implications of its own. If properties and relations are just concepts that people apply to particulars, that implies that the particulars wouldn't have them anymore if the people weren't there to apply them. For example, without someone around to say it or think it, strawberries wouldn't be red, Mount Everest wouldn't be bigger or more massive than a hydrogen atom, and this wouldn't be a sandwich. If a tree falls in a forest and no one's around to hear it, there's no such thing as a tree, a forest, or a sound. That also seems weird. Resemblance nominalism is an alternative, and it sort of flips the script. These things don't look like each other because they're all sandwiches. They're sandwiches because they all look like each other, because they resemble all the other sandwich things. That's fairly appealing for fans of Occam's Razor because we don't need a third element to explain the relationship between sandwiches anymore, rather than having a panini and a grilled cheese and a universal or concept through which they resemble each other, they just do. But we also lose something by appealing to resemblance as the basis of all properties, the sense that there's a certain way in which things resemble each other. Resemblance nominalism has difficulties with groups of objects that have more than one thing in common. If I went around and stamped every single sandwich in the universe with a certain QR code, I wouldn't have any grounds to say that being stamped with the code was different than being a sandwich, because they'd call out the same group of objects that resemble each other. I know that I could stamp non-sandwiches with the code and create a different group, but I don't really have an easy way to say why QR code-ness is different from sandwichness, the way a Platonist might. A more recent version of nominalism, trope theory, tries to negotiate a middle ground between the weirdness of universals and the uncomfortable implications of abandoning them entirely. Tropes are like universals in that they're abstract objects, so they're still weird, but rather than manifesting in multiple places at once, tropes are unique to the particulars they're attached to, the redness and sweetness tropes of this strawberry, the mass trope of this particular hydrogen atom. Instead of a universal sandwichness that sandwiches everywhere participate in, each individual sandwich has a separate and unique sandwich trope. In fact, for trope theorists, all that particulars are are bundles of tropes. So what does that get you? Actually, quite a bit. We don't have to deal with universals being in multiple places at the same time, because tropes only ever happen in one place. The similarities we see in those particulars are explained as resemblances between tropes. There's a sandwich trope of this panini, there's a totally distinct sandwich trope of that grilled cheese, yet another sandwich trope for this PB&J. Those tropes all resemble each other, and that's why all sandwiches are alike. But how do tropes resemble each other exactly? It seems we're back where we started in a way. We're left trying to explain what it is exactly that the sandwich tropes have in common. I mean, resembling other tropes is a property, so we could use the same process again. The panini and PB&J sandwich tropes have a trope of resembling each other, so do the grilled cheese and the panini tropes. But those tropes also resemble each other, and those tropes resemble each other. Hmm. Each of these categories of thought has its own variations in diversity of opinion, and even philosophers who belong to the same category might disagree about certain peculiar situations, but most would agree that the problem of universals is a nuanced and difficult question, where even the least complicated answers have vastly unintuitive implications. And that's partly why the hot dog sandwich debate and debates like it have persisted for so long and will continue far into the future. If you really want to figure out what position you ought to hold, you'll have to engage with some of the oldest questions about the fundamental nature of human perception, thought, and reality itself. Talk about nerd sniping. By virtue of what do you think that sandwiches are alike? Please leave a comment below and let me know that you thunk. Thank you very much for watching. Don't forget to bob off the side while I share. And don't stop thunking.