The philosophy of the Principia Cybernetica Project also finds its basis in what we call
"physical constructivism". While constructivism is traditionally known in
its mathematical context, including the denial of reductio ad
absurdum proofs, the existence of actually infinite objects, and the law
of the excluded middle{As described more elsewhere , cite{TUV87a} is a
constructive philosophy of mathematics from the perspective of Principia Cybernetica.}
Cyberneticians especially have championed a broader interpretation
that extends to psychology and the general philosophy of science.
Psychological constructivism asserts that knowledge is constructed by the
subject, and not a simple "reflection" of or correspondence to reality.
Following especially Kant, the neural mechanisms of the sense organs, the
cortex, and the entire brain are seen as active mediators which provide the
inherent "categories of perception". It follows that perception and
knowledge are in fact a model of reality, and not merely a reflection
or impression of it.
We can also describe an extreme version of radical constructivism, which is
currently fashionable with some cyberneticians, but which we reject.
Some radical constructivists approach strong skepticism by denying the existence
of any external reality, and simply define reality as our
knowledge. This "brain in a vat" view is unnecessarily strong. Instead we
take a kind of agnostic view, which is a-realist, not anti-realist.
While it is true that knowledge provides no direct and incorrigible access
to the world, and it is not justified to make strong inferences about
reality on the basis of knowledge, at the same time it is not allowed to
make inferences about reality on the basis of a lack of knowledge:
ignorance of something does not entail its non-existence.
We accept mathematical and psychological constructivism, but we go further.
We call our evolutionary philosophy physically constructive in the
sense that systems can only be understood in terms of the (physical)
processes which manifest them and by which they have been assembled. This is
certainly true for physical and biological systems, but also holds for
formal, symbolic, and semantic systems. In particular, we hold that
semantics, language, and mathematics must always be understood in the
context of the physical basis of their operation---on the physical systems
(e.g. sense organs, brains, machines, computers) which transmit, receive,
and especially interpret physical tokens.
