Historical Constraints and the Evolution of Development 1033
Consider ordinary linguistic usage for the following scenario: a favored or
orthodox theory undergirds the basic research program of a discipline—the usual
situation that Kuhn (1962) calls "normal science" as practiced under the influence of
a reigning paradigm. All scientists know, of course, that rare episodes of transition
between explanatory systems, often occurring with sufficient speed and upset—both
structural (to theories) and emotional (to practitioners)—to be deemed revolutionary,
mark our most interesting times. Moreover, nearly all scientists, if not utterly devoid
of ambition or intellectual verve, regard the development of a new explanatory
system as the highest form of achievement in their profession. Nonetheless, the full
working careers of most scientists proceed in the usual mode of research within a
basic paradigm—a "good life" full of interest and intellectual excitement, as any rich
paradigm features forests of unsolved puzzles, and byways (or even substantial roads)
of expansion and originality.
Within such a ruling theory, a set of accepted causes and mechanisms operates
to yield a range of outcomes specified as permissible. (When too many inexplicable
results become well documented outside this permissible range, ruling theories
become strained, and an interesting time of theoretical transition may soon be at
hand.) Now, as a purely linguistic point, what should we call a set of anomalous
results that would not have occurred if our reigning theory held the dominant or
exclusive sway usually granted to its precepts? What, for example, would we say
about our inability to turn mercury into gold if our causal theory proclaimed the
possibility of so doing, or (to choose a case of expansion rather than restriction) what
would we call our newfound ability to generate living insects from decaying flesh if
our theory dictated that only plants, but not animals, could originate by spontaneous
generation?
We might, of course, eventually abandon our old theory for a novel system of
explanation. But what if we do not choose to do so, at least not yet, and especially if
we know that our theory really does work well, and as specified, for a large range of
well documented cases? We would have to acknowledge that the old theory does not
enjoy so wide or exclusive a domain of application as we had previously asserted.
What would we then call the classes of exceptions—particularly the results of
unorthodox causes that forced us to accept limitations upon the old beliefs? We
generally label such exceptions as "constraints" because they restrict the range and
power of our orthodox explanations.
I regard this conceptual meaning of constraint—the imposition of limits upon
the range of orthodox theories by documentation of exceptions and demonstration of
unorthodox causes—as undeniably "positive" in the important intellectual and
psychological sense that any scientist worth his salt must cherish such upsetting
discoveries for the conceptual challenges thus unleashed. Thus, if the Darwinian
functionalism of natural selection acts as a reigning theory, then any documented
constraint from internal channeling of variation—whether positive or negative in the
empirical sense discussed in the last section—must be viewed as intellectually
positive for questioning our orthodoxy and documenting something new and
interesting that shouldn't