“What is in the territory that gets onto the map? [...] What gets onto the map, in fact, is difference.
A difference is a very peculiar and obscure concept. It is certainly not a thing or an event. This piece of paper is different from the wood of this lectern. There are many differences between them, [...] but if we start to ask about the localization of those differences, we get into trouble. Obviously the difference between the paper and the wood is not in the paper; it is obviously not in the wood; it is obviously not in the space between them .
A difference, then, is an abstract matter.
Difference travels from the wood and paper into my retina. It then gets picked up and worked on by this fancy piece of computing machinery in my head.
… what we mean by information — the elementary unit of information — is a difference which makes a difference.
(from “Form, Substance and Difference”, Nineteenth Annual Korzybski Memorial
Lecture delivered by Bateson on January 9, 1970, under the auspices of the Institute of General Semantics, re-printed from the General Semantics Bulletin, no.
37, 1970, in Steps to an Ecology of Mind (1972))
This “difference which makes a difference” statement is quite famous, although sometimes considered only a figure of speach.
I think it is not, let me show you why!
For me a difference can be interpreted as an operator which relates images of the same thing (from the territory) viewed in two different maps, like in the following picture:
This figure is taken from “Computing with space…” , see section 1 “The map is the territory” for drawing conventions.
Forget now about maps and territories and concentrate on this diagram viewed as a decorated tangle. The rules of decorations are the following: arcs are decorated with “x,y,…”, points from a space, and the crossings are decorated with epsilons, elements of a commutative group (secretly we use an emergent algebra, or an uniform idempotent right quasigroup, to decorate arcs AND crossings of a tangle diagram).
What we see is a tangle which appears in the Reidemeister move 3 from knot theory. When epsilons are fixed, this diagram defines a function called (approximate) difference.
Is this a difference which makes a difference?
Yes, in two ways:
1. We could add to this diagram an elementary unknot passing under all arcs, thus obtaining the diagram
Now we see four differences in this equivalent tangle: the initial one is made by three others.
The fact that a difference is selfsimilar is equivalent with the associativity of the INVERSE of the approximate difference operation, called approximate sum.
2. Let us add an elementary unknot over the arcs of the tangle diagram, like in the following figure
called “difference inside a chora” (you have to read the paper to see why). According to the rules of tangle diagrams, adding unknots does not change the tangle topologically (although this is not quite true in the realm of emergent algebras, where the Reidemeister move 3 is an acceptable move only in the limit, when passing with the crossing decorations to “zero”).
By using only Reidemeister moves 1 and 2, we can turn this diagram into the celtic looking figure
which shows again four differences: the initial one in the center and three others around.
This time we got a statement saying that a difference is preserved under “infinitesimal parallel transport”.
So, indeed, a difference makes four differences, in at least two ways, for a mathematician.
If you want to understand more from this crazy post, read the paper :-)