D. M. MACKAY 
THE SCIENCE OF COMMUNICATION 
The central notion of the science of communication is that of 
information-flow. Information is said to flow from A to B when 
the (spatiotemporal) form of some happening at A determines 
the form of another at B, without necessarily supplying the 
energy for it. ‘Thus we say that the caller who presses the front 
door bell-push ‘“‘sends information”? to the kitchen, because 
the form of his action has determined the form (in this case the 
timing) of the ringing of the bell, regardless of where the 
necessary energy came from. 
By analysing the logical process by which a form is determined, 
it has proved possible to define useful numerical measures of 
““information-flow’? which have given a new precision to 
communication science in recent years!; but for our present 
purpose it is sufficient to recognize the qualitative distinction 
between explanations in these terms and those in terms of 
traditional physics. One could say that whereas physics looks 
for explanations in terms of the dependence of force upon force, the 
science of communication constructs its “causal chains” out 
of the dependence of form upon form. 
To the embarrassment of its practitioners, no satisfactory 
name has yet been devised for this new science. The term 
“‘cybernetics”’, coined in 1834 by André Ampére to denote the 
“science of government”’’, and used by Norbert Wiener? to 
describe the science of control and communication in the animal 
and the machine, has recently gathered so many woolly asso- 
ciations that it finds limited favour. 
Systems whose functioning depends on information-flow are 
termed “‘information systems’’. By abstracting the information- 
flow map of such systems we can often discern important 
common features in extremely diverse situations—as diverse, 
for example, as a self-guided missile, a human limb, and a 
national economy. Instead of loose appeals to analogy, it 
then becomes possible to apply common scientific principles 
in our efforts to understand or regulate these different situa- 
tions. 
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