Okay. I am going to assume that the attempt to discover a foundation for ethics in the refutation of transcendental solipsism the impossibility of a private language, the idea of following a rule and Wittgensteinian forms of life is dead in the water.
In Totality and Infinity Emmanuel Levinas cites Descartes' argument from the 'idea of infinity' as the model for his case for the necessity of recognition of the Other, the face that commands me, that forbids murder, the Other to whom I am perpetually (so long as I exist on this planet) in ethical debt. I thought I could see a connection here with my idea of the authority of others to correct my judgements (hence 'what seems right' to me in attempting to follow a rule for the use of a word is different from the question what is right). Now I see this as wishful thinking. The weakest link.
Hence: there is a world of others, without doubt, the world of you, or, better, they. But no Other, no Thou. These are fine things to believe, but I don't see any way to argue the case. See this as analogous to Kant's rejection of the ontological, cosmological and teleological proofs of the existence of God in order to 'make room for faith'.
What I'm saying is that ethics is in exactly the position Kant claimed for the belief in God. A worthy object of faith, nothing more. My concern is with what is capable of proof in metaphysics (if anything!). Just like Kant. And I don't mind at all that I am following the same itinerary. The point is, the dialectic is not the same.
Standing on the shoulders of philosophers spanning nearly a quarter of a millennium, I can see something that Kant missed: His focus on the metaphysic of experience was wrong. The only basis for a coherent metaphysical theory, as I have argued ever since I wrote my doctoral thesis The Metaphysics of Meaning is a metaphysic of action.
This is Rorty territory (Philosophy and the Mirror of Nature). But the philosopher whose work is closest to what I have in mind is John Macmurray (The Self as Agent). Macmurray believed that 'All meaningful knowledge is for the sake of action, and all meaningful action is for the sake of friendship.' I accept the first proposition, as the foundation stone of the metaphysic of action. The second is merely an expression of faith, worthy though it may be.