The paper discusses different definitions of agricultural sustainability and claims that one has to be cautios about the normative content of the definition of sustainability. Therefore different groups in society may have different perceptions of agricultural sustainability, which is why the paper explores a conceptual model of a farm in its surroundings from the perspective of discourse theory. The farm is understood as a human activity system that reflects on the different, conflicting perceptions of agricultural sustainability. The farmer tries to assess how the current management is performing in relation to strong discourses in society, which may impact on the farm. For this use the farmer needs indicators of among others resource use and environmental impact. Examples of such indicators used in a so-called Ethical Account" are given.