The leading question of this paper is: Where does the normativity of the ethics of science and technology come from? This is a challenging question given that the traditional reservoirs of convenience (like metaphysical universalism) are no longer at our disposal the way they used to be . The paper is divided into eight sections: (1) It is specified what challenges a non-foundationalist justification and normativity has to meet . (2) A three-dimensional conception of responsibility is developed based on the human triangular I–We–World relations . (3) The concepts of bounded responsibility and bounded ethics of science and technology are formulated . (4) The principle of reflective equilibrium is introduced as a principle of rationality, and it is shown how this principle generates rational and reasonable justifications in the ethics of science and technology . (5) Against this background, a reconception of internal and external responsibilities of science is given . (6) The type of responsibility demanded is exemplified by today ’ s climate research . (7) The paper argues for a hand-in-hand model of uncertainties in the sciences and for ethical obligations to preserve the conditions of human life on earth . The ethical argument is spelled out in terms of ethical care, preservation, and precaution . (8) Additionally, some arguments are developed to answer the question of why it is reasonable at all to preserve human life on earth.