Reading is not natural in the way speech is. Children learn to talk without lessons, but every reader had to be taught, and writing is only about five thousand years old, far too recent for the brain to have evolved for it. Reading works by putting brain areas built for other jobs, such as recognizing objects, to a new use. The scholar Maryanne Wolf, in Proust and the Squid (2007) and Reader, Come Home (2018), builds a warning on this point: because the brain's reading circuit is built by practice, the kind of reading we practice shapes the circuit we end up with.

What deep reading is

Wolf uses the phrase deep reading for the slower work that goes beyond decoding words: making inferences, testing an argument, connecting a text to what we already know, imagining another person's point of view and reflecting. These take time. Her worry is that a lifetime of skimming feeds, headlines and messages trains a different habit. Eye-tracking studies of web pages, such as those by the usability researcher Jakob Nielsen in 2006, found that people often scan in an F-shaped pattern: across the top, partly across a little lower, then down the left side. That suits a list of search results. It does not suit a philosophical argument.

Paper and screen

Does the medium matter? A 2018 meta-analysis by Pablo Delgado and colleagues pooled 54 studies with about 170,000 participants and found that informational texts were understood somewhat better on paper than on screens. The advantage was larger under time pressure and, surprisingly, grew rather than shrank between 2000 and 2017. One explanation is that people approach screens with a skimming mindset and overestimate how well they have understood. The effect is modest, and for narrative texts the difference was negligible. Screens also have real advantages, such as adjustable type for readers with poor eyesight and instant access to books for people far from any library.

Old advice for a new problem

Worry about too much reading material is old. In the first century AD the Roman philosopher Seneca advised his friend Lucilius to stay with a few great authors rather than sampling everything. In Richard Gummere's 1917 translation he writes, "Everywhere means nowhere," and compares the restless reader to a traveler who has many acquaintances but no friends. His warning is against sampling many authors without staying with any. In 1854 Henry David Thoreau wrote in Walden that "Books must be read as deliberately and reservedly as they were written." Both describe something readers must choose to do, because no medium does it for them.

Some popular history about reading needs correcting. A famous passage in Augustine's Confessions, written around 400, records his surprise that Bishop Ambrose read without speaking. In Edward Pusey's translation, "his eye glided over the pages, and his heart searched out the sense, but his voice and tongue were at rest." It was long taken as proof that silent reading was rare in the ancient world. Many scholars now argue that silent reading was not unusual among skilled readers in antiquity; what struck Augustine may have been that Ambrose read silently in front of visitors who hoped to talk to him. Reading habits have always varied, and changes in them are nothing new.

Practicing depth

In 1940 the philosopher Mortimer Adler published How to Read a Book, which describes levels of reading. In paraphrase, they are elementary reading, to understand the sentences; inspectional reading, a quick, systematic skim to learn what a book is about and how it is built; analytical reading, a thorough reading that asks what the book says and whether it is true; and syntopical reading, comparing many books on one subject. His point fits today well. Skimming is a legitimate tool when chosen on purpose as a first step, and it becomes harmful when it is the only way a person reads. Deep reading is a skill like any other. It grows with regular practice on texts a little harder than comfortable, in conditions free of interruption.

Worked example: a hard essay

Jonah must read a twenty-page essay on free speech for a seminar. His habit is to scroll through it on his phone between other tasks, which leaves him with a vague impression and little else. This time he tries a plan. He spends five minutes on inspectional reading: title, headings, first and last paragraphs, to learn the shape of the argument. Then he prints the essay, since the research suggests paper may help with dense informational text, and he reads it in two forty-minute sessions with his phone in another room. He writes one sentence in the margin for each section saying what it claims, and a question wherever he disagrees. Afterward he can state the author's main argument in his own words and name its weakest step. His plan follows Adler's order, a deliberate skim and then a deep reading, and it honors Thoreau's advice to read as deliberately as the author wrote.