compress; the information that (for instance) the inside of my oven is too hot for infants to live comfortably is really only interesting if there is an infant (or something sufficiently like an infant) in the vicinity of my oven. If there isn’t, that way of describing my oven’s state remains accurate, but ceases to be very relevant in predicting how the system containing the over will change over time; in order for it to become predicatively relevant, I’d need to change the state of the system by adding a baby (or something suitably similar). This is a consequence of the fact that (as we saw in 1.5), the business of the special sciences is two-fold: they’re interested both in identifying novel ways of carving up the world and in applying those carvings to some systems in order to predict their behavior over time. Both of these tasks are interesting and important, but I want to focus on the latter one here—it is analysis of the latter task that, I think, can serve as the foundation for a plausible definition of ‘complexity.’
By removing the person from our example system, we reduce the complexity of that system. This is relatively uncontroversial, I take it—humans are paradigmatic cases of complex systems. My suggestion is that the right way to understand this reduction is as a reduction in the number of predictively useful ways the system can be carved up. This is why the distinction just made between special-scientific compression and useful special-scientific compression is essential—if we were to attend only to shifts that changed a system enough for a particular special science’s compression to fail entirely, then we wouldn’t be able to account for the uncontroversial reduction of complexity that coincides with the removal of the human from our kitchen-system. After all, as we just saw, the fact that the compression scheme of biology is useless for predicting
- Of course, these two interests are often mutually-reinforcing. For a particularly salient example, think of the search for extraterrestrial life: we need to both identify conditions that must obtain on extrasolar planets for life to plausibly have taken hold and, given that identification, try to predict what sort of life might thrive on one candidate planet or another.