Scientific discovery has long been explained in terms of theory, data,
and little else. We propose a new approach to scientific discovery in
which tools play a central role by suggesting themselves as scientifi
c theories, by way of what we call the tools-to-theories heuristic of
scientific discovery. In this article, we extend our previous analysis
of statistical tools that became theories of mind to the computer and
its impact on psychological theorizing. We first show how a conceptua
l separation of intelligence and calculation in the early 19th century
made mechanical computation, and later the electronic computer, conce
ivable. We next show how in this century, when computers finally becam
e standard laboratory tools, the computer was proposed-and eventually
adopted-as a model of mind. Thus, we travel the full circle from mind
to computer and back.