My first point concerns ethics, and Habermas's ideas about the discursive redeemability of ethical claims. Here, it seems to me, critical rationalism can improve over Popper's own explicit formulations in the text of The Open Society, by applying to ethical claims the very theory of intersubjective testability that Popper developed, with reference to Kant, in his Logic of Scientific Discovery. Popper's own account of ethics in the text - as opposed to the Addendum - to The Open Society, while admirable in its (Kantian) stress on the autonomy of ethics from command, brute facts, or supposed tendencies immanent within history, is unclear as to how an individual's ethical judgments are constrained - if they are constrained by anything at all. If we introduce, as I would suggest, a closer parallel with the idea of inter-subjective assessment as it occurs within Popper's epistemology, several advantages follow. We avoid any appearance of subjectivism in ethics, and we show how it is that ethical claims are fallible. In addition, we may clarify an aspect of Popper's political thought. For there, Popper appeals to the idea that a broadly negative utilitarian agenda for politics may be generated through intersubjective agreement, while suggesting that other issues - such as the pursuit of positive visions of the good life - must be undertaken by voluntary means. He also works with a conception of the criticism of policy proposals by citizens which, similarly, seems to assume a procedure of intersubjective agreement like that which we find in Popper's epistemology, but which we do not, in fact, find in Popper's explicit writings about ethics in the text of The Open Society.
In addition, this approach provides us with a rationale for treating individuals as something like ends in themselves - because their judgments are the means through which any ethical claim is to be assessed; and their autonomy plays a vital role in this context.
Such an approach may thus draw - from Popper's work - a theory of who should be accorded such respect, and why. In addition, it would allow - through what might be seen as an updating of the moral sense theory of Hutcheson and Adam Smith into afallibilistic form of ethical intuitionism - an alternative path to something like a Kantian ethic. One difference from Kant, however, would be that the content of ethics would be supplied not by pure reason, but by what results when ethical claims, made by individuals, pass through the filter of inter-subjective assessment. Another would be that universality would also have a rather different character. For rather than its having simply to be asserted as a purely formal property of ethical claims, it would come through the acceptability, in principle, of substantive ethical claims, and moral principles, to all moral agents - i.e. those who can engage in critical argument about them. And autonomy - another major concern of Kant's - would come through our recognition of the importance of the protection of the autonomy of individuals to make ethical judgments - because these, as mentioned above, would be the means through which any substantive ethical claim would be assessed.
If we adopt such an approach, more consequences follow than can be explored in a brief note such as this. But one point that is, perhaps, worth spelling out explicitly is that, within it, individuals may have rights both as participants in, and as the objects of reasoned consensus within, ethical argument. Who counts as the former is, essentially, an empirical matter. (This suggests a further improvement over Kant, for whom, as far as I can see, there is no way in which we can identify who a moral agent is, as everything, as it presents itself to us, is on a par in being explicable in purely causal terms, and Kant offers no empirical criterion as to the conditions under which we should introduce a teleological form of understanding, as an Idea of reason). However, there is good reason to suppose that the realm of moral agents - in the sense of those capable of participation in ethical argument - is not co-extensive with the human species. For those apes capable of communication - however imperfect - in American Sign Language would seem clearly to have showed the capacity for participation in such discussions, at least at the level of the descriptive if not the argumentative functions of language. While the foetus, the very severely disabled, and, say, those in the most advanced states of senile dementia, do not possess such a capacity.
I do not wish to claim that there are not important disanalogies between judgement and argument in ethics and in science, some of which I have discussed elsewhere. But I do claim that there are greater parallels than critical rationalists seem customarily to admit of, and that these parallels are suggestive, and would prove a fruitful area for investigation by critical rationalists.