If different political factions prefer different criteria for defining the extension of some common word, rationalists may not be able to say that one side is simply right and the other is simply wrong, but we can at least strive for objectivity in _describing the conflict_. Before shrugging and saying, "Well, this is a difference in values; nothing more to be said about it," we can talk about the detailed consequences of what is gained or lost by paying attention to some differences and ignoring others. That there exists an element of subjectivity in what you choose to pay attention to, doesn't negate that there _is_ a structured empirical reality to be described—and not all descriptions of it are equally compact.
In terms of the Lincoln riddle: you _can_ call a tail a leg, but you can't stop people from _noticing_ that out of a dog's five legs, one of them is different from the others. You can't stop people from inferring decision-relevant implications from what they notice. (_Most_ of a dog's legs touch the ground, such that you'd have to carry the dog to the vet if one of them got injured, but the dog can still walk without the other, different leg.) And if people who work and live with dogs every day find themselves habitually distinguishing between the bottom-walking-legs and the back-wagging-leg, they _just might_ want _different words_ in order to concisely _talk_ about what everyone is thinking _anyway_.
If different political factions prefer different criteria for defining the extension of some common word, rationalists may not be able to say that one side is simply right and the other is simply wrong, but we can at least strive for objectivity in _describing the conflict_. Before shrugging and saying, "Well, this is a difference in values; nothing more to be said about it," we can talk about the detailed consequences of what is gained or lost by paying attention to some differences and ignoring others. That there exists an element of subjectivity in what you choose to pay attention to, doesn't negate that there _is_ a structured empirical reality to be described—and not all descriptions of it are equally compact.
In terms of the Lincoln riddle: you _can_ call a tail a leg, but you can't stop people from _noticing_ that out of a dog's five legs, one of them is different from the others. You can't stop people from inferring decision-relevant implications from what they notice. (_Most_ of a dog's legs touch the ground, such that you'd have to carry the dog to the vet if one of them got injured, but the dog can still walk without the other, different leg.) And if people who work and live with dogs every day find themselves habitually distinguishing between the bottom-walking-legs and the back-wagging-leg, they _just might_ want _different words_ in order to concisely _talk_ about what everyone is thinking _anyway_.