Reply to Nate Soares on Dolphins

A similar definition of intelligence was expressed by Aquinas as “the ability to combine and separate”—the ability to see the difference between things that seem similar and to see the similarities between things which seem different.

—A. R. Jensen

In a June 2021 Twitter thread, Nate Soares, executive director of the Machine Intelligence Research Institute, asserts, “The definitional gynmastics [sic] required to believe that dolphins aren’t fish are staggering.” (Archived.)

Soares elaborates:

Suppose for argument that we adopt the (dubious but sadly common) assumption that words like “fish” should have a genealogical definition. Then, just as whales are mammals, mammals are fish—as you can see by tracing the lineages.

Which is to say, if we look at the least common ancestor of all things that are clearly fish, and define a “fish” to be one of its descendants, then dolphins—and humans, and frogs, and birds—are fish.

Now suppose instead we take this as the reductio ad absurdum that it is, and accept that words like “fish” should be functionally rooted, according to macroscopic human-relevant features.

Then the natural denotation of “fish” is, I claim, the collection of all the swimmy creatures, which clearly includes dolphins.

Indeed, this is quite likely what “fish” used to mean—”Jonah was swallowed by a fish”, etc. etc.

Yet somehow, once we figured out about genealogy, the pedants were like “well actually this fish’s uncle was a fuzzy pigdear, so it’s not actually a fish, you uneducated idiot, you absolute moron” and then we all forgot what “fish” meant out of sheer shame or something???

(I feel a sense of betrayal about this. Usually the pedants are my people! How did it go so wrong?)

So, look: this isn’t about who the fish’s uncle is. When a kid points at a whale and says “look, a fish”, and you’re like “haha no, its tail flaps horizontally and its gradma had hair”, who’s in the wrong here?

But Soares is failing to address the strongest case in favor of phylogenetic definitions, even for vernacular words rather than specialist jargon. It’s true that in most everyday situations, people don’t directly care about which animals are evolutionarily related to each other. But the function of word definitions is not to capture everything the word means. If words were identical with their definitions, and you defined humans as “mortal featherless bipeds”, then you would never be able to identify anyone as human without seeing them die. That doesn’t seem right!

Instead, words express probabilistic inferences in the form of short messages that compress information: if you want to send your friend an email telling them about an animal you saw at the beach, it’s much more efficient to send the 7 ASCII bytes dolphin and trust that your friend knows what dolphins are, than it would be to somehow include all the information your brain has stored about dolphins as an email attachment.

A dictionary definition is just a convenient pointer to help people pick out “the same” natural abstraction in their own world-model. Unambiguous discrete features make for better word definitions than high-dimensional statistical regularities, even if most of the everyday inferential utility of using the word comes from fuzzy high-dimensional statistical correlates, because discrete features are more useful as a simple membership test that can function as common knowledge to solve the coordination problem of matching up the meanings in different people’s heads.

And that’s why phylogenetic categories are useful: because genetics are at the root of the causal graph underlying all other features of an organism, such that creatures that are genetically close to each other are more similar in general. It’s easier to keep track of the underlying relatedness as if it were an “essence” (even though patterns of physical DNA aren’t metaphysical essences), rather than the all of the messy high-dimensional similarities and differences of everything you might notice about an organism.

Soares derides observations about an organism’s “uncle” or “gradma” [sic] as if these were isolated facts of no more general interest, but actually, information about a creature’s evolutionary history is intimately related to everything else there is to know about the organism. It’s not a coincidence that dolphins are warm-blooded, breathe air (despite living in the water!), and nurse their live-born young. We need to formulate the concept of “mammals (including aquatic mammals)” to make sense of that cluster of observations.

But dolphins are also swimmy creatures, like fish, but unlike most mammals, due to the forces of convergent evolution. So dolphins also form a cluster in configuration space with fish, right? Yes! That’s why I keep using the phrase “high-dimensional”: it’s possible for things to be similar in some respects, while simultaneously being different in other respects. The cluster of similarities induced by convergent evolution to the aquatic habitat exists in a different subspace from the cluster of similarities induced by evolutionary relatedness.

Isn’t it reasonable to want a short word for the swimmy creatures (including dolphins), independently of ancestry? Yes, in this I agree with Soares entirely: that’s a reasonable thing to want a common word for, much as we have a word for trees, even though trees are a convergently evolved strategy rather than a taxonomic group. Is it reasonable to want to use fish as that word? Sure, I guess that makes sense, if everyone knows what you mean. And in fact this usage is listed in Wiktionary as the second definition:

fish (countable and uncountable, plural fish or fishes)


  2. (archaic or loosely) Any animal (or any vertebrate) that lives exclusively in water.

I imagine Soares is not too happy with that archaic characterization. (At least it didn’t say proscribed.) If Soares had simply argued that fish(2) (water animals) should become a more popular and accepted usage, then I wouldn’t be writing this reply. But, oddly, Soares advocates not just that fish(2) become a more accepted usage, but for the abolition of the more specific fish(1) (finned cold-blooded vertebrate gill-breathing water animals). Soares writes:

I’m not trying to take away your concepts. You’ve still got words like Vertebrata, Agnatha, and Gnathastomata for when you’re thinking about animals in terms of who their uncle is.

But you are trying to take away the expressive vocabulary of fish(1), which millions of English speakers are already using in that sense. Agnatha (a specific superclass of jawless fish) and Gnathostomata (the infraphylum of jawed vertebrates) are not adequate replacements for fish(1). What is the motivation for this?

Is Soares perhaps suffering from the common misconception that words can only have a single definition? But it’s actually not uncommon for words in natural languages to have more than one (related) meaning, which can be distinguished from context. That’s why dictionaries have multiple numbered definitions under the same word with the same etymology.

For example, water. The word “water” can be used to mean H₂O in any form (in which sense ice is a kind of water), or specifically liquid H₂O (in which sense ice is not a kind of water). If someone says “water” and you’re not sure if they’re using it in the ice-inclusive or the ice-exclusive sense, and ice happens to be relevant to the conversation you’re having, then you might have to ask the speaker for clarification! Fortunately, this doesn’t cause a whole lot of problems among people who are trying to communicate with each other and don’t have an incentive to start a pointless dispute over definitions.

But if someone were to declare that water should only be used in the ice-exclusive sense, and that pedants who want to want to talk about water in the ice-inclusive sense are engaging in “definitional gynmastics” and need to invent a new word for their thing, that would be pretty weird … right?

Frankly, I’m puzzled. Nate Soares, famous autodidact extraordinaire and executive director of the Machine Intelligence Research Institute, is no doubt more intelligent and knowledgable than a humble ordinary programmer like myself. He clearly shares my passion for the philosophy of language. So whatever arguments I can discover, surely he would have already invented independently. So I must be missing something.

Could there, perhaps, be some additional context to this conversation that Soares neglected to make explicit? That seems unlikely, however.

Anyway, this concludes my blog post about why I think it makes sense to use the word fish in the sense of “cold-blooded vertebrate animal that lives in water, moving with the help of fins and breathing with gills” in many contexts, albeit possibly not all contexts. Soares’s work is very important and I’m sure he’s very busy, but since he seems to be so passionate on this issue, I wonder if he could spare a few moments to engage with my arguments? If so, I eagerly await his reply.