5. Rational Behavior. A purpose of social science,
of law, of philosophy has been for a long time to give
meaning to the notion of “rational behavior,” to ac-
count for “irrationality,” to discover, for example in
criminal cases, whether a given individual could be
considered as having acted rationally or not. In general
there appears to exist an intuitive notion of what “ra-
tional” must mean. Frequently this notion would be
based on experience; but experience varies with each
individual, and whether any person has an intuitively
clear idea of “rationality” is doubtful. In the simple
case in which an individual wishes to maximize a
certain quantity, say utility, and provided he controls
all factors or variables on which his utility depends,
then we shall not hesitate to say that he acts rationally
if he makes decisions such that he actually obtains this
maximum, or at least moves stepwise in its direction.
Thus, rationality is predicated on two things: (a) the
identification of a goal in the form of preferences
formed, possibly stated numerically, and (b) control
over all the variables that determine the attainment
of the goal.
The first condition requires that the individual have
a clear notion of what he wants and that he possess
sufficient information which will identify the goal he
wishes to reach. The second condition requires that
the individual be able to determine first the variables,
and second the consequences of the changes he may
make in setting their values for reaching the intended
goal, and finally that he actually can set the values
of the variables as it may appear proper to him. The
amount of foresight demanded (especially if the goal
should be distant) is considerable but this point shall
not be considered further. The control factor, however,
is of primary concern: if nature intervenes in his in-
tended behavior, the individual can control an in-
different nature by means of statistical adjustment; the
farmer, for example, can arrange his planting so that
on the average neither a very dry nor a very wet
summer will hurt him. Whether nature is always in-
different is another question (Morgenstern, 1967). But
it is an entirely different matter if among the variables
there are some that are controlled by other individuals
having opposite aims. This lack of complete control
is clearly the case in zero-sum (winnings compensate
losses exactly) two-person games of strategy, but also
in business, in military combat, in political struggles
and the like. It is then not possible simply, and in fact,
to maximize whatever it may be the individual would
like to maximize, for the simple reason that no such
maximum exists. It is then not clear intuitively which
course of action is “better” than another for the indi-
vidual, let alone which one is optimal.
To determine optimal, or “rational” behavior is pre-
cisely the task of the mathematical theory of games.
Rational behavior is not an assumption of that theory;
rather, its identification is one of its outcomes. What
is assumed is that the individual prefers a larger advan-
tage for himself to a smaller one. If these advantages
can be described and measured and are understood by
the individual, and if he chooses not to pursue the
required course, then there is a limited definition of
nonrational behavior for such situations. It is assumed
that the demonstration (if the theory succeeds) of the
optimal course of action is as convincing to the indi-
vidual as a mathematical proof is in the case of a
mathematical problem. But the theory allows that a
participant may deviate from his optimal course, in
which case an advantage accrues to the others who
maintain their optimal strategies.
Prior to the advent of game theory the term “ra-
tional” had been used loosely as referring to both of
the two conceptually different situations set forth
above, as if there were no difference. The transfer of
the notion of rationality from the completely control-
lable maximizing condition to one in which there is
no exclusive control over the variables is inadmissible.
This has been the cause of innumerable difficulties
permeating much of philosophical, political, and eco-
nomic writing. No side conditions, however compli-
cated, which may be imposed or exist when one is
confronted with a clear maximum problem changes the
situation conceptually. In the case where full control
exists side conditions merely make the task of reaching
the maximum more difficult—perhaps even impossible,
for example, because it may computationally be out
of reach. But even in its most complicated form it is
conceptually different—and vastly simpler—than the
problem faced by, say, a chess player or a poker player,
and consequently by any one whose activities have to
be modeled by games of strategy. The conceptual
difference does not lie in numbers of variables or in
computational difficulties; but we note that the solution
of games becomes extremely difficult both when the
number of strategies is large (even with as few players
as in chess) and also when the number of participants
increases, though each may have only a few strategies.
When there are, say, 100 variables of which one
individual controls 99 the other the remaining one, this
appears to be a different situation from that when there
are only 2 variables and each player controls one. Yet
conceptually the two are identical. No practical con-
siderations, such as possibly assigning weights to varia-
bles, and the like, in an effort to reduce difficulties of
action, will work. The fundamental conceptual differ-
ence and difficulty remains and has to be resolved by
the theory.
