AS A youth in Vienna, Heinz von Foerster’s first claim to fame was as a magician. But more important, and to some people just as magical as his tricks, was his transformation of cybernetics (in the decade around 1970) by insisting that the observer must be taken into account in the description of any system, because he may affect the processes being observed. From this he went on to develop systems to modify the formulation of the systems of classical cybernetics, in an extension of the field that became known as “the cybernetics of cybernetics” or “second-order cybernetics”.

Heinz von Foerster (originally Förster) was born in Vienna, the eldest son of Emil von Förster and his wife Lilith, and educated in philosophy and logic by the Vienna Circle, and in physics at Vienna’s Technical University. He completed his doctorate at the University of Breslau in 1944. His family was distinguished and held a prominent position in the intellectual life of Vienna: friends and relatives included the philosopher Ludwig Wittgenstein, the playwright Hugo von Hoffmansthal, the painter Erwin Lang, and the Wiesenthal family.

The family supported Josef Matthias Hauer, the inventor of an alternative to Schoenberg’s 12-tone technique. His grandfather was architect of the Vienna Ring. He had a brother, Ulrich, and a sister, Erika, and was especially close to his cousin Martin Lang, with whom he studied magic and roamed Austria’s mountains in winter and in summer. In 1939 he married the actress Mai Stürmer, with whom he had three sons.

During the war von Foerster lived and worked in Berlin, where he moved to disguise the Jewish element in his ancestry, and did research in short-wave and plasma physics. At the end of the war he found a way back to Austria, where he worked in the telephone industry while also reporting on art and science for the Austro-American radio station Rot-Weiß-Rot, his communication skills and showmanship flourishing.

Meanwhile, he was working on his book Memory: A Quantum Physical Examination. To promote this, he moved to the United States in 1949, where (with barely a word of English) he was taken up by the mathematician, neuroscientist and philosopher Warren McCulloch, with whom he communicated in the language of mathematics.

The trip was a turning-point. McCulloch was then chairing the Macy Conferences on “Circular Causal and Feedback Mechanisms in Biological and Social Systems” in New York, which were attended by the anthropologists Margaret Mead and Gregory Bateson, the computation theorist John von Neumann and the mathematician Norbert Wiener.

To improve his English, von Foerster was made secretary and editor. His first act was to add “Cybernetics” to the conference title. Together with Wiener’s book Cybernetics (1948), these conferences gave form and substance to the emerging discipline. The study of “circular causality” can now be said to be the real heart of cybernetics.

McCulloch arranged for von Foerster to become director of the University of Illinois tube laboratory. Von Foerster imported his family and lived in Champaign until his retirement in 1976, when he moved into a house that he built himself, with his architect son, above the Pacific outside Pescadero, California.

In 1958 von Foerster founded the Biological Computer Laboratory, attracting considerable funding. As well as a cohort of students, he hosted most of the distinguished scholars in cybernetics for residencies, and the laboratory became the world’s most advanced centre for the development of cybernetic thinking. The first parallel computers were built there, and crucial research was carried out on the fast electronic switching that is critical to today’s computers.

Although von Foerster is known in some circles for his excursion into demographics (when he started lively debate in the journal Science), he was most important for sponsoring radical work in such subjects as the organisation of the living and the foundations of mathematics and logic. He tended to hide his own contribution behind the work of others, but his understanding of the reflexive nature of systems led to profound changes in the understanding of knowledge and of our connection with the world in which we find ourselves. For many he reintroduced the amazement of wonder.

Having held Guggenheim fellowships in 1956-57 and 1963-64, von Foerster won many honours. He was president of the Wenner-Gren Foundation, 1963-65, and of the Society for General Systems Research, 1976-77. He was elected to a fellowship of the American Association for the Advancement of Science in 1980, and in 1996 the University of Vienna made him an honorary professor. Last year he won the first Viktor Frankl Prize. He published some 200 scientific papers and several books, and gave more than a thousand lectures around the world.

He is survived by his wife, Mai, and two sons.

Heinz von Foerster, cybernetician, was born on November 13, 1911. He died on October 2, 2002, aged 90.