Cybernetics was defined by Wiener as “the science of control and communication, in the animal and the machine” — in a word, as the art of steermanshi… - W. Ross Ashby

Further, as every law of nature implies the existence of an invariant, it follows that every law of nature is a constraint.

During the last few years it has become apparent that the concept of "machine" must be very greatly extended if it is to include the most modern developments. Especially is this true if we are studying the brain and attempting to identify the type of mechanism that is responsible for the brain’s outstanding powers of thought and action. It has become apparent that when we used to doubt whether the brain could be a machine, our doubts were due chiefly to the fact that by ‘‘machine’’ we understood some mechanism of very simple type. Familiar with the bicycle and the typewriter, we were in great danger of taking them as the type of all machines. The last decade, however, has corrected this error. It has taught us how restricted our outlook used to be; for it developed mechanisms that far transcended the utmost that had been thought possible, and taught us that ‘‘mechanism’’ was still far from exhausted in its possibilities. Today we know only that the possibilities extend beyond our farthest vision.

Throughout, we shall be exemplifying the thesis of D. M. MacKay: that quantity of information, as measured here, always corresponds to some quantity, i.e. intensity, of selection, either actual or imaginable