I don’t have a good answer for how people do this, at least not without thinking about it for a while. But I think I know several people who are quite good at in practice, so I dispute that ‘you can give a philosophical explanation of how this works’ is a relevant rebuttal.
There is some relevant difference between the practical and the philosophical, where for some particular purpose the lack of “objective” being possible doesn’t matter because you’re not asking for resolution past the point where it’s relevant. As long as you are comfortable with the assumptions you’ve made and don’t wish to question them, this won’t be a concern, and you can make great practical progress despite the lack of firm grounding (as evidenced by the existence of the modern world).
Instead of denying objective truth, can’t you get the same benefit by making your claims precise enough that they only talk about one system?
But where is the ground of even one system to make it objective (rather than intersubjective)?
I don’t have a good answer for how people do this, at least not without thinking about it for a while. But I think I know several people who are quite good at in practice, so I dispute that ‘you can give a philosophical explanation of how this works’ is a relevant rebuttal.
There is some relevant difference between the practical and the philosophical, where for some particular purpose the lack of “objective” being possible doesn’t matter because you’re not asking for resolution past the point where it’s relevant. As long as you are comfortable with the assumptions you’ve made and don’t wish to question them, this won’t be a concern, and you can make great practical progress despite the lack of firm grounding (as evidenced by the existence of the modern world).