Sustainable development may be defined as a non-declining value of capital stocks (social, natural, built and human) over time. The ability for substitution between and within each stock over time has been widely debated, resulting in the identification, and then preservation of 'critical capital stocks'. We propose that 'critical' can be defined from two ethical perspectives; teleological or consequentialist (goal or ends based) and deontological (moral duty and rule based). The consequential ethic ensures critical capitals are 'utilitarian' in value and they generate goods and services for the maintenance of human wellbeing. Whilst deontologically critical capital depends on culturally and psychologically 'protected' values, which may vary locally or at least (as for, e.g., biodiversity) be open to conflicting opinions. This separation in the basis for defining critical capital stocks leads to awareness that some tradeoffs between critical capital stocks may be irreconcilable or likely to lead to outrage. A framework is developed to guide practitioners as to how to identify critical capital stocks using both protected and utilitarian values. Examples show that 'protected' values are likely to be specific to community (ethnic, religious, cultural, etc.) and require different methods for resolving substitutability of capital stocks to achieve sustainable development.