The extended mind theory doesn’t just change the way we think about the mind. It also changes how we judge what’s good and bad about today’s mind-altering technologies. There’s nothing unnatural about relying on the Internet—Google and all—for information. After all, we are constantly consulting the world around us like a kind of visual Wikipedia. Nor is there anything bad about our brains’ being altered by these new technologies, any more than there is something bad about a monkey’s brain changing as it learns how to play with a rake.

Neuroscientists will soon be able to offer fresh ways to enhance our brains, whether with drugs or with implants. To say that these are immoral because they defile our true selves—our isolated, distinct minds—is to ignore biology. Our minds already extend out into the environment, and the changes we make to the environment already alter our minds.

That doesn’t mean we must approve of every possible extension of the mind, and even good extensions will have some drawbacks. Socrates worried that writing would make people forgetful and unwise. Sure enough, writing did rob us of some gifts, such as the ability to recite epic poems like The Iliad from memory. But it also created a much larger pool of knowledge from which people could draw, a pool that has continued to expand.