In contemporary debates on risk in modern societies, on reflexive modernity and a general crisis of knowledge, concepts and terms such as ignorance, non-knowledge or negative knowledge are used to denote that there can be knowledge about what is not known. Many of these terms are not only used with different meanings, sometimes antithetic to one another in their implications, but they often propose tree-like taxonomies without broaching the issue of the further connectivity of different types of unknowns between the limbs of the tree. In this article, an attempt is made to simplify and integrate different connotations in sociological usage of concepts that try to grasp the unknown and to outline the dynamic and recursive relations of these types of knowledge and the way they can change over time. This is illustrated with examples from large-scale ecological design projects.

Experiments are generally thought of as actions or operations undertaken to test a scientific hypothesis in settings detached from the rest of society. In this paper a different notion of experiment will be discussed. It is an understanding that has been developed in the classical tradition of the Chicago School of Sociology since the 1890s, but has so far remained unexplored. This sociological understanding of experiment does not model itself strictly on the natural sciences. Rather, it implies a process of societal self-experimentation without a fixed setting of a sociological experimenter. The paper discusses this notion of experiment in relation to the recursive dependency of the application and the production of sociological knowledge. It is contended that this concept of a self-experimental society offers theoretical insights that could well prove fruitful for a sociological concept of experiment beyond the realm of the laboratory.

The concept of real-world experiments is a framework to understand environmental design projects under real world conditions. Contrary to laboratory experiments that are generally thought to exclude the public, real-world experiments involve combinations of social and natural factors. In this paper the theory of real-world experiments is applied to the fieldwork of ecological restoration. The case discussed here is an ecological design process at Montrose Point, a peninsula built on landfill in Lake Michigan on the North Side of Chicago. It illustrates how, in the practice of ecological restoration, the idea of experiment can be understood as being built on processes of recursive learning that include different parts of the wider society and nature. The paper outlines a concept of robust implementation strategies in which public involvement is a pivotal part of a more encompassing activity of ecological practice. This is undertaken to aim at a better understanding of learning processes taking place in natural and social systems.