formal description of the argument I think you're making (though of course you weren't arguing for a proposition at all). You're right, it's not begging the question. The general knowledge offered in the original position thought experiment specifies that I could be any human person. 8 week fetuses are human persons Therefore in the original position thought experiment, I must consider the possibility that I am an 8 week fetus. Therefore I should legislate against abortion of 8 week fetuses. So my issue with this is that anyone who would grant you the premise that "8 week fetuses are human persons" would already have no problem with the conclusion, without you getting all fancy with thought experiments. So why bring it up? "it seems to have nothing to do with the original position thought experiment." Don't be too sure. Of course Rawls thought of the original position in the way I described, with people making decisions that will affect them. In -- in principle -- there's nothing to stop anyone sitting down at that board table, provided they understood that they were not to favour anyone. But this question would really take us off track here (as I think the main track is the one below). "Therefore I should legislate against abortion of 8 week fetuses." No. I mean yes, of course I think that, but no, that's not at all what I said or meant here . You're projecting an argument that was never made or implied. My point