The difference between knowledge that is actionable and knowledge that is sterile builds on a well-known distinction made by the philosopher Gilbert Ryle (1949). Ryle argued that actionable knowledge has two components, know how and know that. Know how is akin to practical experience, know that to abstract information. Without the requisite know how, know that has limited usefulness. With only know that, you might talk a good game, but you would never be able to play one. To play you need know how. And we learn know how, Ryle argues, through engaging in the relevant practices.

This argument suggests that knowledge you can put into practice curiously comes out of practice. New ideas and inventions are spun out of a practice and circulate most readily among people who share that practice. These claims may appear to violate several almost sacred tenets about human knowledge. For example, on their face they seem to deny the importance of theory. In fact, they do not. Theorizing is important. But it is also, as Ryle argues, just another form of practice-the practice of theorizing. Here, as anywhere else, practical experience counts for a good deal.

The importance of a shared practice to the creation and circulation of knowledge also seems to deny the primacy of the individual in the creation of knowledge. The individual genius and lone inventor is a cherished figure. Yet it does not detract from geniuses to note the ways in which they drew on (and inspired) collaborators and competitors. Shakespeare, for example, worked at the center of a group of quite exceptional London dramatists. At different times, members of this group collaborated. They also all stole willfully from one another. (Consequently, there is a great deal of work that cannot easily be attributed to an individual author.) Simultaneously, they all competed, driving each other to greater and greater heights. None of this limits Shakespeare's towering genius. Similarly, the early impressionists as a group experimented with radical innovations in the world of painting, working together, driving each other, and providing a sympathetic audience for each other while the public at large could make no sense of what each was up to. None of this lessens Monet's achievements.

Nor will such arguments offend those familiar with modern scientific or high-tech innovation, who have long associated major breakthroughs with clusters of names: Watson and Crick; Shockley, Bardeen, and Brattain; Gates and Allen; or Jobs and Wozniak, for example. Moreover, in almost all of these cases, the known names in fact stand for much larger groups of unacknowledged collaborators.