Some contemporary Thomists have the idea that there are exactly three metaphysical species—three kinds differentiated by qualitatively different natures—of living things: plants (maybe broadly understood as non-sentient living things), mere animals, and rational animals.
Here’s a line of thought that yields two-thirds of the view, starting with a premise that most medieval Aristotelians would have accepted:
Our (metaphysical) species is rational animal.
Therefore, if there were a rational fish, it would be a member of our species.
And, a fortiori any rational ape would be a member of our species.
So, all rational fish would be the same species as all rational apes.
If all rational fish would be the same species as all rational apes, all non-rational fish are the same species as all non-rational apes.
The above generalizes from fish to all other animals.
So, all rational animals are the same species and all non-rational animals are the same species.
I don’t have an argument for 5, but it seems pretty plausible.
And the claim that all living non-sentients are the same species doesn’t seem implausible given 7.
I myself reject 1.
3 comments:
2, 3, and 5 feel plausible if we are allowed to think of the features fish, rational and ape, rational as analogous to round, red. (Roundness and redness do not exclude each other.) But I doubt we are allowed to do this.
The genus-species definition of fish has to have this form:
An animal that is χ
and the definition of an ape, this form:
An animal that is π,
where χ and π are specific differences. (Whether χ=π is the main question at hand, so leave that open.)
Now, either χ and π exclude rationality or not. If they exclude rationality, then a rational fish has to lack χ and a rational ape has to lack π. And that would undercut premise 5 of your argument. I would expect that χ and π do exclude rationality, because something about fish and ape nature has to determine the following normative features: a fish’s inability to syllogize is not a handicap; an ape’s inability to syllogize is not a handicap. And this cannot be the fact of their animality! (Similar considerations about normativity would give independent reasons for thinking χ≠π.)
But even if χ and π do not exclude rationality, I’m not sure we can assume that χ=π. We might suppose that candidate features for specific differences are stacked up in some way: If the animal is rational, then its rationality plays the role of the specific difference; if not, then that role devolves to some other feature. If χ excludes π, then they wouldn’t necessarily have to be ranked with respect to each other. If χ doesn’t exclude π, then we could just say that one is ranked higher than the other.
I suppose another way to think about this--inspired by your final comment--is that in rational animals, the non-rational features are less important than in non-rational animals, so the non-rational features are less likely to differentiate kinds. Less important in two ways. First, they are *relatively* less important, in the sense that they are a smaller part of the whole package, because rationality is such a big part of the package. Second, and more interestingly, because rationality changes the way of life to such a degree that the characteristic lives of a rational fish and a rational primate become quite similar. After all, notice how rational primates can spend months underwater (by making a submarine) and presumably rational fish would be able to spend months on land in some similar way.
Still, it seems like a weird taxonomy where at the top level we subdivide animals into rational and non-rational, and then on the non-rational side we subdivide into, say, vertebrate and invertebrate, but on the rational side we don't subdivide into vertebrate and invertebrate.
It doesn’t feel too weird to me, because rationality allows us to form the concept of the good in a universal way (to think about what it would mean for something to be the good as such), and so it allows us to order our lives explicitly in relation to the good. (By externalizing my reasons in speech or writing, I am able to reflect on those reasons and ask whether they are *good* reasons, and this act of reflection, iterated, drives me towards higher principles, chief of which is simply *the* good.)
Lower animals can perceive in ways that allow them to perceive and pursue particular goods but not to order represent the way those things could be ordered to a universal good. So we would expect their characteristic flourishing to be more fragmented or refracted than ours.
Admittedly, those are a lot of commitments on my part that many people wouldn’t share.
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