typically needs rather simple behavior for us actually to be able to identify overall rules that let us make reasonable predictions about it.

Yet in fact even in living organisms such behavior is quite common. And for example particularly in lower animals there are all sorts of cases where very simple and predictable responses to stimuli are seen. But the point is that these are normally just considered to be unavoidable reflexes that leave no room for decisions or freedom.

Yet as soon as the behavior we see becomes more complex we quickly tend to imagine that it must be associated with some kind of underlying freedom. For at least with traditional intuition it has always seemed quite implausible that any real unpredictability could arise in a system that just follows definite underlying rules.

And so to explain the behavior that we as humans exhibit it has often been assumed that there must be something fundamentally more going on—and perhaps something unique to humans.

In the past the most common belief has been that there must be some form of external influence from fate—associated perhaps with the intervention of a supernatural being or perhaps with configurations of celestial bodies. And in more recent times sensitivity to initial conditions and quantum randomness have been proposed as more appropriate scientific explanations.

But much as in our discussion of randomness in Chapter 6 nothing like this is actually needed. For as we have seen many times in this book even systems with quite simple and definite underlying rules can produce behavior so complex that it seems free of obvious rules.

And the crucial point is that this happens just through the intrinsic evolution of the system—without the need for any additional input from outside or from any sort of explicit source of randomness.

And I believe that it is this kind of intrinsic process—that we now know occurs in a vast range of systems—that is primarily responsible for the apparent freedom in the operation of our brains.

But this is not to say that everything that goes on in our brains has an intrinsic origin. Indeed, as a practical matter what usually seems to happen is that we receive external input that leads to some train of thought which continues for a while, but then dies out until we get