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This work explores the consequences of Heinz von Foerster's claim in the context of linear signal theory, embodiment and the creation of artifacts that the nervous system is operationally closed. It operates only in contact to itself.

In linear signal theory all transfer functions can be directly associated with the neural activity where also the environment is described by neural activity. The phenomenon of embodiment is interpreted from the perspective of the nervous system, thus from the inner perspective. To identify inside and outside an organism must learn to identify the disturbances which are only in the environment. This can be done by anticipatory learning.

Questions whether the nervous system is able to distinguish between inside and outside. Mathematically stays in the field of linear control theory and tries to give this mathematical formalism a new meaning in the light of radical constructivism. Gives some guidelines how to apply the highly theoretical claims to more practical situations.

Provides further evidence of the important contribution to the theory of constructivism made by Heinz von Foerster.

The purpose of this paper is to apply virtual agonist–antagonist mechanisms (VAAMs) to robot joint control allowing for muscle-like functions and variably compliant joint motions. Biological muscles of animals have a surprising variety of functions, i.e. struts, springs and brakes.

Each joint is driven by a pair of VAAMs (i.e. passive components). The muscle-like functions as well as the variable joint compliance are simply achieved by tuning the damping coefficient of the VAAM.

With the VAAM, variably compliant joint motions can be produced without mechanically bulky and complex mechanisms or complex force/toque sensing at each joint. Moreover, through tuning the damping coefficient of the VAAM, the functions of the VAAM are comparable to biological muscles.

The model (i.e. VAAM) provides a way forward to emulate muscle-like functions that are comparable to those found in physiological experiments of biological muscles. Based on these muscle-like functions, the robotic joints can easily achieve variable compliance that does not require complex physical components or torque sensing systems, thereby capable of implementing the model on small-legged robots driven by, for example, standard servo motors. Thus, the VAAM minimizes hardware and reduces system complexity. From this point of view, the model opens up another way of simulating muscle behaviors on artificial machines.

The VAAM can be applied to produce variable compliant motions of a high degree-of-freedom robot. Only relying on force sensing at the end effector, this application is easily achieved by changing coefficients of the VAAM. Therefore, the VAAM can reduce economic cost on mechanical and sensing components of the robot, compared to traditional methods (e.g. artificial muscles).

The paper serves as an introduction to the special issue on Heinz von Foerster. Major episodes of his life are sketched and related to his scientific convictions regarding transdisciplinary research and radical constructivist. In the second part the contributions to the issue are summarized. Finally, the relevance of Foerster's work is discussed.

The arguments are based on the scientific literature.

Foerster argued against reductionist science and in favor of transdisciplinary research in order to trigger further scientific developments.

By using transdiciplinary and choosing the constructivist perspective, science will increase its productivity. This should be reflected in science policy.

By pointing at the variety of his scientific output and his influence on many colleagues and students, the paper is in support of Foerster's non‐reductionist worldview.