The Homebrew Computer Club, out of which Apple and many other Silicon Valley startups came during the 1970s, speaks—as does the free‐​software movement—to the continued vigor of collective invention today. Collective invention, in short, is privately profitable. How?

If we follow economist W. Brian Arthur in modeling growth as the consequence of a rearrangement of ideas, the sharing of ideas becomes propitious.29 If 10 individuals each produce one idea and if those 10 individuals each share their ideas, then—for the cost of generating only one idea—each individual gets access to many potential combinations of new ideas. For example, there would be 10!/(10 − 3)!3! or 120 possible combinations of 3 out of the 10 contributions and 252 ways of combining 5 together. These different potential combinations could supply each of the 10 individuals with much personalized scope for private profit.

But how does a player access the knowledge of others? Only by doing his own research. Much scientific knowledge is tacit (not capable of being understood simply by reading but only by continual experience or social interaction); therefore, only active researchers possess the tacit knowledge by which to assess the research of others.30 This degree of excludability, coupled with the access to others’ knowledge, provides a private incentive to do research.

We can therefore remodel the research game from a prisoner’s dilemma into one in which players can access the research of others only if they make research contributions of their own. We call research in this new model a “contribution good.”31 Participants no longer fear that their ideas will be picked up and used by others. Rather, they fear that other potential contributors will not be sufficiently numerous to create a vibrant and potentially profitable field. Participants will welcome newcomers to a growing technical field rich in spillovers.

This mathematical formalization of research as a contribution good reflects researchers’ behavior in real life. The sociologist Robert Merton, for example, characterized research with the four imperatives, including communism, universalism, disinterestedness, and organized skepticism (CUDOS), where communism represents the mutual contribution of knowledge and disinterestedness represents Merton’s belief that researchers apparently act selflessly.32 The Merton paradox (for researchers are as self‐​interested as anyone else) is resolved by understanding research as a contribution good, where researchers do work to acquire the tacit knowledge by which to access the research of others, and it’s the hope of copying that incentivizes research; it doesn’t disincentivize it.