philosophically it might be possible to say that my world view is built on a foundation of sand
More like your world view is no more (or less) 'reasonable' than that of the Sabbath-keeper. You both have perfectly consistent reasons, starting from your own premises. So you can't, I think, criticise the Sabbath-keeper for being 'unreasonable'. What you really mean is not that they have no reasons for keeping the Sabbath, but rather that their reasons derive from premises which you think are factually false.
And yes, it's a pity that people arguing from different premises can't really have much of a debate; but it's still useful to identify when that's the case, as otherwise lots of time can be wasted with people talking past each other as if they could have such a debate, only to find out that they were arguing from different premises all along.
(How does one test the truth of ethical premises? The best way I've found is to push them to their logical conclusions and see if you can derive something clearly wrong. To believe in the truth of utilitarianism, for example, I think you need to find some way of stopping your position logically leading to you becoming Peter Singer.)
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philosophically it might be possible to say that my world view is built on a foundation of sand
More like your world view is no more (or less) 'reasonable' than that of the Sabbath-keeper. You both have perfectly consistent reasons, starting from your own premises. So you can't, I think, criticise the Sabbath-keeper for being 'unreasonable'. What you really mean is not that they have no reasons for keeping the Sabbath, but rather that their reasons derive from premises which you think are factually false.
And yes, it's a pity that people arguing from different premises can't really have much of a debate; but it's still useful to identify when that's the case, as otherwise lots of time can be wasted with people talking past each other as if they could have such a debate, only to find out that they were arguing from different premises all along.
(How does one test the truth of ethical premises? The best way I've found is to push them to their logical conclusions and see if you can derive something clearly wrong. To believe in the truth of utilitarianism, for example, I think you need to find some way of stopping your position logically leading to you becoming Peter Singer.)
S.