Thinking and Deciding

32 THE STUDY OF THINKING
Descriptive models are theories about how people normally think — for example,
how we solve problems in logic or how we make decisions. Many of these
models are expressed in the form of heuristics, or rules of thumb, that we use in
certain situations. One heuristic is the “What if everyone did that?” rule for thinking
about moral situations, and another is the use of analogies in making predictions.
Other descriptive models are mathematical, describing functional relationships between
inputs (such as probabilities) and outputs (such as choices or judgments).
In the probability problem that I just described, the heuristic used is to judge
probability by asking, “How similar is this sequence to a typical sequence?” Because
the sequence G B G B B G is more similar to the typical sequence than B G B B B B,
the former is judged more likely. Like most heuristics, this is a good rule to follow
in some situations, and we can “understand” why: When other things are equal, an
item that is similar to the members of a category is more likely to be in that category
than an item that is not similar to the members. (Here the “category” is “sequences
of births.”) But that argument does not apply here because the type of similarity that
people perceive is irrelevant in this case. In sum, heuristics can lead to errors when
they result from incomplete understanding.
Unlike many other fields of psychology, such as the study of perception, where
the emphasis is on finding out “how it works,” much of the study of thinking is
concerned with comparing the way we usually think with some ideal. This difference
from other fields is partly a result of the fact that we have a considerable amount of
control over how we think. That is not so with perception. Except for going to the
eye doctor once in a while, we have very little control over how our visual system
works. To answer the question “How do we think?,” we also have to answer the
question “How do we choose to think?” The way we think is, apparently, strongly
affected by our culture. Such tools as probability theory, arithmetic, and logic are
cultural inventions. So are our attitudes toward knowledge and decision making.
Thus, the way we think is a matter of cultural design. To study only how we happen
to think in a particular culture, at a particular time in history, is to fail to do justice to
the full range of possibilities.
Part of our subject matter is therefore the question of how we ought to think. If we
know this, we can compare it to the way we do think. Then, if we find discrepancies,
we can ask how they can be repaired. The way we ought to think, however, is not at
all obvious. Thus, we shall have to discuss models or theories of how we ought to
think, as well as models of how we do think. Models of how we ought to think will
fall, in our discussion, into two categories: prescriptive and normative.
Prescriptive models are simple models that “prescribe” or state how we ought to
think. Teachers are highly aware of prescriptive models and try to get their students
to conform to them, not just in thinking but also in writing, reading, and mathematics.
For example, there are many good prescriptive models of composition in books on
style. There may, of course, be more than one “right” way to think (or write). There
may also be “good” ways that are not quite the “best.” A good teacher encourages
students to think (or write) in “better” ways rather than “worse” ones.