Natural kinds across categories

Most philosophical discussions of natural kinds concern entities in the category of substance: particles, chemical substances, organisms, etc. But I think we shouldn’t forget that there is good reason to posit natural kinds of entities in other categories.

For instance, you and I are each engaging in a token activity that falls under the natural kind (say) mammalian breathing. The natural kind specifies some essential properties of the kind, namely that it is a kind of filling and/or emptying of the lungs, as well as some teleological features, such as that the filling and emptying should be rhythmic. Instances of the kind may be better or worse: given that I am congested after a long drawn-out cold, likely your breathing is better than mine.

There are, plausibly, such things as natural activities, which fall under activity natural kinds. These may kinds may include gravitational attraction, mating, fish respiration, etc.

Dispositions, too, may fall under natural kinds, indeed a nested sequence of them. We might say that some dispositions are habits, and some habits are virtues. Thus, perhaps, you and I each have a certain disposition to rationally withstand danger, a disposition that is a token of courage, a kind of virtue. Your and my courages are different: for instance, perhaps, I am more willing to withstand social danger while you are more willing to withstand physical danger. Whether indeed virtues are natural kinds seems to me to be a central question for the metaphysics of virtue ethics.

There may be natural kinds of relations, too. Thus, I think marriage is a natural kind. On the other hand, I think presidency is not.

How I learned to be a bit less judgmental about social distancing

Earlier in the pandemic, I was very judgmental of students hanging around outside in groups and not respecting six-foot spacing. Fairly quickly I realized that it is inadvisable for the university to rebuke students for doing this, since such rebukes are likely to lead to their taking such interactions to private indoor venues, which would be much worse from a public health standpoint. But that practical consideration did not alleviate my strong judgmental feelings.

Eventually, however, these observations have made me realize that in our species, there is a natural desire to spend time in relatively close physical proximity to each other. And indeed, this is quite unsurprising in warmblooded social animals. Realizing that social distancing—however rationally necessary—requires people to go against their natural instincts has made me quite a bit less judgmental about noncompliance.

It took observation of others to realize this, because apart from practicalities, I find myself to prefer something like two meter spacing for social interaction with people outside my family. Greater physical distance from people outside my family has been quite pleasant for me. A conversation at two meters feels a little bit less stressful than at one meter. But looking at other people, it is evident that my preference here is literally unnatural, and that for other people such distancing is quite a burden.

Of course, sometimes it is morally necessary to go against one’s natural desires. It is natural to flee fires, but fire fighters need to go against that desire. And in circumstances where it is morally necessary to go against natural desires, people like me who lack the relevant natural desires are particularly fortunate and should not be judgmental of those for whom the actions are burden.

Natural event kinds and Frankfurt cases

Choices are transitions from an undecided to a decided state. Suppose choices are a natural kind of event. Then only the right sort of transition from an undecided to a decided state will be a choice.

Here, then, is something that is epistemically possible. It could be that a choice is a kind of thing that can only be produced in only one way, namely by the agent freely choosing. Compare essentiality of evolutionary origins for biological kinds: no animal that isn’t the product of evolution could be a lion. Of course, one can have something internally just like a lion arising from lightning hitting a swamp and one can have a transition from an undecided to a decided state arising from a neuroscientist’s manipulation, but these won’t be a lion or a choice, respectively.

If this is right, then it seems no Frankfurt story can make a choice unavoidable. For to make a choice unavoidable, an intervener would have to be able to cause a choice in case the agent wasn’t going to do it. In other words, there will be no Frankfurt argument against principle of alternate possibilities:

• If x chose A, then it was causally possible for x not to have chosen A.

This is rather flickery, though: it doesn’t require that x could have chosen non-A.

Person is not a natural kind

1. God is not a member of any natural kind.

2. If person is a natural kind, then every person is a member of a natural kind.

3. God is a person.

4. So, person is not a natural kind.

Animals

Suppose that somewhere in the galaxy there is a planet where there are large six-legged animals with an inner supportive structure, that evolved completely independently of any forms of life on earth and whose genetic structure is not based on DNA but another molecule. What I said seems perfectly possible. But it is impossible if animals are simply the members of the kingdom Animalia, since the six-legged animals on that planet are neither DNA-based nor genetically connected to the animalia on earth.

On the other hand, the supposition that somewhere (maybe in another universe) there is water that does not have H₂O in it is an impossible one. So is the supposition that there are horses without DNA.

So the kind animal is disanalogous to the kinds water and horse. The kind water is properly identified with a chemical kind, H₂O, and the kind horse is properly identified with a biological species, Equus ferus. But the kind animal does not seem to be properly identified with any biological kind.

One can have DNA-based animals and non-DNA-based animals. If the Venus fly-trap evolved the ability to move from place to place following its prey, it would be an animal, but still a member of Plantae. Animals are characterized largely functionally, albeit not purely functionally, but also in reference to the function of their embodiment—there cannot be any animals that are unembodied.

Is animal a genuine natural kind? Or is it a non-natural kind, constructed in the light of our species’ subjective interests? I don’t know. I take seriously, though, the possibility that there is an "Aristotelian" philosophical categorization that goes across biological categories.

Talk video: Marriage is a natural kind

I just noticed that my recent SCP talk arguing that marriage is a natural kind has been posted. Slides (which I think don't show up on the video) are here.

Role kinds

Some kinds of roles succeed in imposing norms on those in roles of that kind. For instance, friends should help each other because they are friends, and spouses should be faithful to each other because they are spouses. Other kinds of roles do not succeed in imposing any norms. If I hurt you, I cannot rationalize my action by saying that I did that because I was your enemy. That may be an explanation, but being an enemy imposed no norm on me. At most it imposes merely apparent norms (before Socrates, the Greeks thought you should treat your enemies badly--they were wrong). What makes the difference? What gives some roles the genuine normative power they have?

Here is a natural law hypothesis I am attracted to. There are some natural human roles, and they each impose norms on those who fill them. I've in effect argued that spouse is one of those roles. Some other plausible examples: parent, child, friend, authority, subject of authority. Our nature specifies a potentiality to such roles, and gives them their normative power. There is a classificatory hierarchy between the natural roles. Spouse is a sub-role of friend, for instance. (An interesting and controversial question: are husband and wife natural sub-roles of spouse? If so, there will be further norms to being a husband and to being a wife.) And then all roles that have normative power are either natural roles or sub-roles specialized on the scaffolding of one or more natural roles, inheriting all their normative power from the natural roles. For instance, the roles of president and monarch are socially constructed sub-roles of authority, and their normative power over those in the role entirely comes from the role of authority. What about the normative power of the role over other people? That I suspect actually comes from the other people having the roles of citizen or subject, respectively, which are both sub-roles of the natural role of subject of authority. Being a monarch spouse is, on the other hand, a constructed sub-role of two different roles: monarch and spouse. (Think here of object oriented languages with multiple inheritance.) And while spouse is natural monarch is a constructed sub-role of authority.

In the above, I was talking about roles considered as general types, like spouse or parent or monarch. These types have tokens: spouse of Bill, parent of Joey, monarch of Canada. One can think of these token roles as also sub-roles, specializations of the role. An interesting question: is there any token role that is natural? That would be a token role whose normative force comes not just from the type role that it is a token of, as when being a spouse of Bill gets its normative force from being a spouse of someone-in-general. I think one plausible case is when the role is with respect to God. Being a subject of God may be a natural role. (What about friend of God? Perhaps that, too, but there the relevant nature may be a grace-nature.)

We can ask some interesting structural questions. Is there a highest level natural role? Perhaps being human or being a person. I have in the past speculated that it might be friend, but I now think that's mistaken, because friend roles are tied to particular individuals, while some of the other roles are not: an authority need not change qua authority when subjects are replaced by others (through conception, death and migration), but a friend does change in respect of friendship when friends come and go.

And how is this all tied to love? I suspect like this. Love isn't itself a role. But the roles determine which form one's love should take. Maybe in fact that is how they exercise their normative force, and that is what explains why there can't be a natural role such as enemy.

Marriage is a natural kind

I just posted the slides from my SCP Midwest talk on marriage as a natural kind.

The possibility of unicorns

Kripke argued that it is not possible for there to be unicorns. For "unicorn" is a natural kind term. But there are many possible natural kinds of single-horned equines that match our unicorn stories, and there is no possible natural kind that has significantly more right to count as the kind unicorn. So none of them count, and no possible world contains unicorns.

But there is another approach, through vagueness and supervaluationism. Let's say that the term "unicorn" is vague. It can be precisified as a full description of any one of the possible natural kinds of single-horned equines that match our unicorn stories.

Now consider the sentence that Kripke is unwilling to assert but which seems intuitively correct:

1. Possibly there is a unicorn.

We get to say (1) if we can correctly affirm:

2. Definitely, possibly there is a unicorn.

And we certainly do get to say this. For (2) holds if and only if:

3. For every precification U of "unicorn", possibly there is a U.

And assuming that all the precifications of "unicorn" are natural kinds that are possibly instantiated (we don't allow as a precification of "unicorn" something whose eyes are square circles, etc.), (3) is true. And so even if there is no world at which definitely there is a unicorn (though there might be—maybe that world is very rich and contains animals that fall under all possible precifications of "unicorn"; Blake McAllister suggests a multiverse), it is definite that there is a world at which there is a unicorn.

Inductive inferences across kinds

I observe some ravens, and they are all black. This gives me good reason to think all ravens are black. This is an inductive inference within a natural kind. One might have this picture of the inductive inference here: observing the ravens, we learn something about the appropriate-level universal raven that they fall under. One might then think that all inductive inference is like this: We observe instances of a genuine, non-gerrymandered natural kind K, and conclude that the kind is such-and-such.

But I don't think this is all that happens. Here are a few other kinds of cases.

1. From the fact that octopi behave in some ways like we do, we infer that they are conscious. But there is no biological taxon K that contains both octopi and humans such that we have good reason to think that all Ks are conscious. The lowest level taxon containing octopi and humans is the subregnum Bilateria and we have little reason to think all Bilateria are conscious. We might seek for a natural kind that isn't a taxon, like critters that exhibit apparently intelligent behavior. But that's a gerrymandered kind. We might try for a non-gerrymandered kind, like critters that exhibit intelligent behavior, but then we would have to have reason to think that octopi exhibit intelligent behavior rather than merely apparently intelligent behavior, and our problem would return.
2. We have good reason to think that all life on earth descends from a single ancestor. But organism on earth isn't a natural kind.
3. We can do induction within artificial kinds. That all the pens that I have observed have ink in them gives me reason to think all pens have ink. But pen isn't a natural kind.

Does this matter? Maybe. (I think a theist may have a better explanation of why induction not-within-a-kind works than a naturalist. But the thoughts here are inchoate.)

Marriage and natural kinds

On a New York Times blog, Wedgwood has offered an interesting argument for same-sex marriage. The argument is focused on what he calls "the 'social meaning' of marriage", which "consists of the understandings and expectations regarding marriage that almost all members of society share." He notes that this meaning "cannot include any controversial doctrines", but rather must include only uncontroversial assumptions about the nature of marriage. He then argues that same-sex couples have the same interest in having access to an institution that yields the same understandings and expectations as heterosexual couples do. Therefore, the social meaning needs to be shifted in such a way as to give access to marriage to same-sex couples. (This quick summary doesn't do full justice to Wedgwood's rich piece.)

But now compare the social meaning of "marriage" to the social meaning of "water", defined by the understandings and expectations regarding water that almost all members of society share.

There is indeed such a social meaning of water. And this social meaning of water may well help fix the meaning of the word "water". But it does not fix the meaning on its own, as we see from Twin Earth cases. On Twin Earth, suppose, there are beings like us, with a language like ours, and they have a substance that behaves just as water does, and hence obeys the same ordinary understandings and expectations that water does, but its chemical structure is instead XYZ.[note 1] The Twin Earthers' word "water" does not refer to H₂O, but to XYZ, even though their word "water" has the same social meaning as our word "water" does. Thus, the meaning of the word "water" is not exhausted by the social meaning of water.

If we focus on social meaning as central to meaning, we're going to say something like: "The word 'water' refers to that natural kind in the vicinity of the word's users that best fits with the users' 'understandings and expectations.'" In other words, the meaning of "water" isn't fixed by the social meaning alone: it is fixed by social meaning plus facts about what natural kinds are really exemplified in the vicinity of the speakers. Moreover, water will have non-obvious essential properties, such as that its molecules are a union of two atoms with atomic number 1 with one atom with atomic number 8. We aren't going to find these properties by examining the social meaning of water.

Now go back to marriage. If "marriage" is analogous to "water", the social meaning of marriage does not by itself fix the meaning of the word "marriage". Rather, "marriage" refers to that natural kind of relationships in the vicinity of the speakers that in fact best fits with the language-users' understandings and expectations. But then we would expect marriage to have all sorts of essential properties that go beyond the social meaning. And it could turn out that the only natural kind of relationships in the vicinity that fits with our understandings and expectations also has the essential property of being a union of a man and a woman.

I take it that Wedgwood is assuming that marriage is unlike water, that the meaning of marriage is exhausted by its social meaning rather than there being a mind-independent natural kind for the word "marriage" to refer to. But whether this is so is the most fundamental question in the debate, and he gives no case his view on it.

A less deep problem with Wedgwood's line of thought is that, as he himself acknowledges, a part of the shared understanding of marriage is that sexual activity is a normal aspect of marriage. But if same-sex sexual activity is not permissible, then same-sex couples do not have the same interest in an institution that comes along with an assumption of normative sexuality, since it is generally not in one's interest that people assume one is doing something impermissible (whether or not one is actually doing it). Thus, Wedgwood's argument requires that same-sex sexual activity is permissible. But his typical philosophical or theological opponent will deny this permissibility.