Of course, it is important to plan ahead, but postponing decisions until the
point of action can simplify the thought processes: Many alternatives that
would have had to be thought of ahead of time will turn out not to be relevant.
Moreover, the physical structures available in the world can then guide the
selection of relevant choices.
Approaches to reasoning and planning that rely heavily upon thought, and
therefore internal information, run into fundamental problems:
.Lack of completeness:In most real tasks, it simply isn’t possible to know
everything that is relevant..Lack of precision:Thereisnowaythatwecanhaveprecise,accuratein-
formation about every single relevant variable..Inability to keep up with change:What holds at one moment may not ap-
ply at another. The real world is dynamic, and even if precise, complete
information were available at one point in time, by the time the action is
required, things will have changed..A heavy memory load:To know all that is relevant in a complex situation
requires large amounts of information. Even if you could imagine learning
everything, imagine the difficulty you’d have finding the relevant stuff
just when it is needed. Timely access to the information becomes the bot-
tleneck..A heavy computational load:Even if all the relevant variables were known
with adequate precision, the computational burden required to take them
all properly into account would be onerous.
The negative side of this is that these world-based decisions must be made
and actions must be taken quickly, which can cause oversimplification and in-
complete analysis. We all know that actions taken in haste are often wrong
actions. With time pressures, there is limited opportunity to consider alterna-
tives or to reflect upon all of the consequences. Clearly, we need to plan ahead,
but not to follow those plans rigidly. We need to respond to the situation, to be
flexible in the face of unexpected occurrences, to change our activities as the
world dictates.
In the World, Impossible Things Are Impossible
The world has an important property: In the real world, it is not possible to do
actions that are not possible. This sounds trivial and obvious, but it has some
profound implications when we move into the artificial world of cognitive
artifacts. Thus it is certainly not trivial to those who write computer programs
that mimic the world. Much of the effort of writing programs that simulate the
world must be devoted to ensuring that the simulation cannot do impossible
things.
I have flown in extremely sophisticated simulations of aircraft, ones that
barely could be distinguished from the real thing. These professional simu-
lators were constructed from real cockpits, they vibrated and sounded like real
planes, and moved about two meters in all directions so they could simulate
most of the body sensations. And when you looked out the window, you saw
theappropriatesights.Yes,theplanesbehavedjustright.ButIonceflewina
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