By the nineteenth and twentieth centuries, the idea that reality was to be understood in terms of physical properties or substance had lost some popularity in favor of systems views involving symmetries, chaos, emergence, complexity, dynamic processes, networks, and relations expressed in formal theories. Researchers discovered systems that purportedly explained everything from molecular properties to plate tectonics and economics. As an effect of the overall excitement, the distinction between the model and the modeled was sometimes missed. This was the case in cognitive science, where researchers often treated formal systems as not just models of cognition but also constitutive of cognition.
Developments in quantum physics led to doubts about how we could know an objective physical reality independent of us. A series of discussions started with the Copenhagen interpretation of quantum mechanics by the Danish physicist Niels Bohr (1885-1962). This interpretation roughly states that quantum mechanics—for conceptual reasons—fails to provide a true picture of reality. This is because quantum mechanics deals with nonclassical physical phenomena, but all we have to wrap our minds around those phenomena are classical interpretations. Postmodernist attacks on science and the so-called science wars thrived on this sort of skepticism.