My concern is not cladistics. It’s with the idea that the lack of sharp boundaries is supposed to undermine the idea of the “realness” of some group. I am not objecting to the biological system of classification (I’d be happy to agree the clade fish is real), I am arguing for the idea of some sort of physical realness to methods of categorization even despite it having to involve some degree of arbitrariness at the boundaries. No, not at the fundamental level. At the fundamental level everything is just quantum fields or whatever, but things don’t have to be real at the fundamental level to be real, or to matter to us, or to have real-world consequences we have to deal with and can’t just pretend isn’t of any value or consequence and we just have to convince ourselves is some sort of illusion of our perception.
You argued at length by drawing from an analogy using colors that color groups aren’t real, because they can in principle blend into each other over infinitely many gradations. That is the reason you stated for why color groups aren’t real. And so the decision of where one group begins and another ends would have to be totally arbitrary. The idea seems to be that if there is not sharp dividing line in principle then the group isn’t real.
But I do think some groups are real, even if there is no actual sharp dividing line between them. At the very least there is something physically real about the phenomenon in question that lends itself to a more intuitive categorization. How things in reality are colored, for example, seems to lend itself to some sort of categorization: As I argued before, many objects in our surroundings are relatively uniformly colored, and while colors are part of some huge space of possible colors that don’t have obvious or clear boundaries, rarely do we find real things that are perfectly uniformly colored all possible colors in equal amounts.
The world is in many cases such that while there isn’t a perfectly sharp boundary between things (areas in light and areas in shade), there is a relatively narrow transition zone where one part shifts gradually into another but much larger area in relatively uniform illumination or shade. In such cases the distribution of light lends itself in an intuitive sense to categorization. This part A is “in shade” provided by the trunk of that tree, that part B is not, and the transition zone C between them occupies a much smaller area.
The exact dividing line is an arbitrary decision to a degree, but I think any reasonable person would have to admit it would not make sense to put the dividing line right in the middle of the letters A or B, and while the exact spot you pick for a dividing line is arbitrary to a degree, it would be “natural” to put it somewhere in C (which could be even more narrow).
In other instances the natural world is much more blurry, and the areas in more uniform illumination are much smaller and the transition zones much broader. In some instances there seems to only be these areas where no obvious boundary is discernible. The shadow on the left of B has a much more blurry edge. Presumably one could have endless arguments about where to draw the line there, and reasonable people have lots of space for disagreement. So not everything lends itself obviously and intuitively to categorization. And it comes in degrees. Some things are totally ambiguous, some are less so, and some are such that essentially everyone who isn’t mentally ill can agree on the distinctions.
So if we return to the case of fish, we can see that even here there is some sense of arbitrariness involved. Even here we have to decide on how far back that clade should go, and we do that by picking characters shared among some collection of organisms and not shared by others. And we can know that this apparent dividing line of characters is a product of fossilization and extinction. That there was, once upon a time, organisms in existence that would have blurred out that dividing line between ancestor and descendant. Hence just like with colors, organisms exist on some conceivably infinite spectrum of anatomical traits that usually doesn’t exist in reality. Nevertheless, despite this arbitrariness of where exactly the clade fish first began, we nevertheless do have the distribution of characters in extant and fossil organisms that we do(in a way similar to how things in our surroundings are colored), and this distribution lends itself to categorization. So the clade fish is real. At least real enough that we can reliably identify it’s members and non-members.
And I think we can say similar things about the categories male and female. Going back to the shadow analogy, I think many more people fall into the A and B parts than into C, and while the distinction would ultimately have to be arbitrary, I think that for purposes where having such categories becomes important (for matters of law, policy, health care and what have you), we’re going to have to decide where to put that line. And just flat out denying that those categories refers to something real isn’t a reasonable alternative.