Carr includes other case studies: He describes doctors who become so reliant on decision-assistance software that they overlook subtle signals from patients or dismiss improbable but accurate diagnoses. He interviews architects whose drawing skills decay as they transition to digital platforms. And he recounts frightening instances when commercial airline pilots fail to perform simple corrections in emergencies because they are so used to trusting the autopilot system. Carr is quick to acknowledge that these technologies often do enhance and assist human skills. But he makes a compelling case that our relationship with them is not as positive as we might think.

All of this has unmistakable implications for the use of technology in classrooms: When do technologies free students to think about more interesting and complex questions, and when do they erode the very cognitive capacities they are meant to enhance? The effect of ubiquitous spell check and AutoCorrect software is a revealing example. Psychologists studying the formation of memories have found that the act of generating a word in your mind strengthens your capacity to remember it. When a computer automatically corrects a spelling mistake or offers a drop-down menu of options, we’re no longer forced to generate the correct spelling in our minds.

This might not seem very important. If writers don’t clutter their minds with often-bizarre English spelling conventions, this might give them more energy to consider interesting questions of style and structure. But the process of word generation is not just supplementing spelling skills; it’s also eroding them. When students find themselves without automated spelling assistance, they don’t face the prospect of freezing to death, as the Inuits did when their GPS malfunctioned, but they’re more likely to make errors.

The solution might seem to be improving battery life and making spelling assistance even more omnipresent, but this creates a vicious cycle: The more we use the technology, the more we need to use it in all circumstances. Suddenly, our position as masters of technology starts to seem more precarious.

Relying on calculators to perform arithmetic has had similar risks and benefits. Automating the time-consuming work of multiplying and dividing large numbers by hand can allow students to spend time and energy on more complex mathematical subjects. But depending on calculators in classrooms can also lead students to forget how to do the operations that the machines perform. Once again, something meant to expedite a task winds up being an indispensable technology.

The phenomenon is not specific to modern technologies; the same concern appears in Plato’s Phaedrus, where a character in the dialogue worries about the effects of the phonetic alphabet: “This discovery … will create forgetfulness in the learners' souls, because they will not use their memories; they will trust to the external written characters and not remember of themselves.” Automating almost any task can rob us of an ability.