An exceedingly common opinion runs as follows:
Certain beings, though conscious/sentient, ‘lack reason’, and it is thus reasonable to treat them in a different way to ‘rational’ beings. These beings without reason include all non-human animals, humans up until a certain (disputed) age, and some (again, disputed) groups of adult humans, who lack the rationality of ‘normal adults’.
Because these beings lack reason, they should not be accorded certain rights, in particular the rights to personal autonomy (others can decide their lifestyle for them) and to political participation (they can’t vote, run for office, etc).
They have, on the other hand, certain privileges: they may have diminished liability for their own (perhaps criminal) actions, they may have a claim on support by others, and their right to protection from harm may be taken more seriously – although in practice often none of these obtain.
I don’t want to straight-out attack this position, I just want to make it seem less necessary, to suggest that there might be an alternative to it, which doesn’t go so far as to ignore or dismiss the (striking) differences we can observe between, say, a 2-year-old and a 22-year-old.
So distinguish two ways of expressing that difference. The first, described above, is to speak of an intrinsic incapacity in one side (usually assumed to be the 2-year-olds), who are in themselves, not rational, and so any deliberation process they engage in won’t produce decisions worth paying attention to.
Now, this claim implies the following: that we and infants can’t engage in the sort of dialogue required for political participation or recognition of autonomy – the sort where views on a topic can be not only exchanged but supported – where the question ‘and why do you think that?’ can be heard and responded to.
This latter claim is weaker, in that it could be true (A and B can’t converse) without it being because one side or the other is fundamentally ‘non-conversant’ or ‘non-rational’. After all, the same lack of dialogue often obtains between two adults who don’t speak the same language, or in bad conditions, or when one is just being a dick because they see no reason not to.
Now, these two conclusions one might draw – the weak conclusion ‘I don’t know how to converse with X’ and the strong conclusion ‘X is incapable of rational conversation’ – will largely agree in practice. If you can’t talk about it, you’ll have to do something else.
But they differ in that the former leaves open the possibility that X might be capable of dialogue with someone else, or that in the future (or the past) dialogue might become possible, once one side or the other learns the relevant ‘language skills’. And this gives support to efforts that might bring us closer to such a point (e.g. to study the communication methods already used on either side).
Maybe these possibilities are implausible for 1- or 2-year-old children. But those aren’t the hard cases. 8-year-old children, wolves, monkeys and parrots are the hard cases. ‘Mentally disabled’ adults are the very hard cases.
In such hard cases, the idea that ‘lacking reason’ is a contingent relational phenomenon, more akin to a failure of interpretation than to a simple lack on one side or the other, seems to me perfectly plausible.
Certainly, the agnostic position, that it may turn out to be such a phenomenon, seems reasonable, especially if you think mainstream knowledge has in the past tended to under-estimate the complexity and versatility of many people’s minds, rather than over-estimate it.
You might also like to avoid making committments on very obscure and difficult subjects like what it’s like to be a dolphin or what rationality actually is.
Anyway, like I said, this might not make a large or immediate difference in practice. But it’s a slightly different and m0re cautious way to express the observations in question, for people who think caution is warranted.