Technological Understanding and Ethics Readiness of Technology: the role of understanding and timing in the ethics of quantum technologies Eline de Jong Abstract: Quantum technologies form a new and rapidly developing family of technologies with wide-ranging potential applications – from breakthroughs in materials science and drug discovery to GPS-independent navigation and novel ways of securing or breaking digital communications. Their emergence has prompted an ethical discussion motivated by the ambition to do things right from the start. Such early-stage engagement with the ethical dimensions of technology, however, comes with a distinctive epistemic challenge: how can we ask meaningful ethical questions about a technology we are only beginning to understand, under conditions of profound uncertainty about what it will ultimately be capable of? This thesis investigates the epistemic conditions of meaningful ethical engagement with technology, using quantum technologies as a paradigm case of new and emerging science and technology. It argues that meaningful ethical discussion – discussion grounded in what a technology actually is and may do – requires two conditions: sufficient understanding of the technology and appropriate timing of ethical engagement. Two concepts are developed to elucidate these conditions: technological understanding and ethics readiness. The first part develops a philosophical account of technological understanding. Drawing on the philosophy of science, technological understanding is defined as a cognitive skill: the ability to recognise how to use a technological artefact to achieve an aim. The account is contextual: different forms of engagement with technology (design, operation, innovation) require different types and degrees of understanding. For ethical engagement specifically, it is understanding of a technology’s functional capabilities – what it can do and may be used for – that is most directly relevant. This functional understanding provides the basis for tracing potential impact and identifying ethical stakes. The second part develops the framework of ethics readiness, which holds that the appropriateness of different ethical approaches depends on the maturity of the technology in question. Meaning-oriented approaches – examining the visions and expectations attributed to a technology – are best suited to early-stage development, while outcomes-oriented approaches gain feasibility and relevance as the technology matures. This framework is applied to quantum computing, quantum sensing, and quantum communication, and put to work in ethical analyses of visions of quantum computing, the Quantum for Good initiative, and the quantum cyber security threat. Together, these two concepts illuminate the epistemic conditionality of ethics of technology and provide the conceptual tools for asking the right ethical questions at the right moment – keeping ethical engagement grounded in technological reality while navigating the uncertainties that inevitably surround new and emerging technologies.