Now consider a case in which it is natural to speak of ``information flow''. The manner in which the diaphragm of a certain microphone is vibrating carries information about what a certain announcer is saying. The modulation of the electromagnetic signal arriving at a certain antenna carries information about the way in which that microphone diaphragm is vibrating. And finally, the modulation of the elecromagnetic signal arriving at the antenna carries information about what the announcer is saying, for instance, ``Nancy Reagan is irritated''.
How does the modulation of the electromagnetic signal at the antenna carry information about the words the announcer spoke? Let's look at the constraints and connecting facts that are involved.
The first constraint we call 
: If the diaphragm
of a micro phone vibrates in a certain way ( 
), then the
announcer's voice produced certain sounds ( 
), given that
the announcer was speaking into the mike ( 
).
The connecting fact, that the announcer was speaking into the
microphone we call 
.
The second constraint we call 
: if the
electromagnetic signal reaching the antenna is of a certain type
( 
), then the diaphragm of the microphone vibrates in a
certain way ( ), given that the antenna and the microphone
are connected in a certain way ( 
).
The connecting fact, that the antenna and the mike are connected in this
way, we call 
.
The third constraint we call 
: if the
electromagnetic signal reaching the antenna is of a certain type
( ), then the announcer's voice produced certain sounds
( ), given that the announcer was speaking into the mike
and that the antenna and the microphone are connected in a certain way
( 
.
The connecting fact, that the antenna, mike and voice are connected in
this way, we call 
.
Let P be the proposition that the announcer said ``Nancy Reagan is
irritated''. Let Q be the proposition that the diaphragm of the mike
in question is vibrating in such and such a way--the way that is the
major constituent of type 
. Then
carries the
information that Q relative to 
, given the
connecting fact .
Moreover, we say that
carries the information that P relative to
, given
.
In such a case, we also say information of type 
flows
along channels of type 
. We
can derive something more like the normal use of the term if we move
to the individual objects, the carriers, that are constitutents of the
connecting types.
We might as well generalize, and state the following principle of information:
(K) There are laws of information flow.
Laws of information flow involve compound infons and relations among
the parameters of those infons. In plain(er) English: laws of
information flow involve relations among states of various components
of information systems, states of various objects remote from those
systems and connections between these. These laws are useful or
exploitable to the extent that these relations and connections are
controllable or at least knowable.
