Walking through the modern public square — by which I mean, of course, the great platforms where the citizenry now does much of its reading and most of its arguing — I am struck less by the quantity of speech than by the curious narrowness of what reaches each reader.

A printer in Philadelphia, in my day, served a town. He could not select his audience; the town selected him. If he printed only what one faction wished to hear, the other faction noticed, and his trade suffered. The discipline of the marketplace, such as it was, kept the press honest in the rough way that markets keep things honest: by punishing the printer whose product served too narrow a constituency.

The modern arrangement inverts the discipline. The platform serves each citizen a slightly different paper, composed of pieces the algorithm believes that citizen will engage with. The discipline of being read by one's political opposites is, in this arrangement, removed. The printer who could not avoid an opposing reader has been replaced by a system that ensures, with considerable subtlety, that the opposing reader is never even shown the page.

I do not propose to ban the practice. I would observe two things only. First, that the citizen who reads only what the algorithm has selected for him reads a press of his own image, and presses of one's own image have, historically, made for poor citizens. Second, that the platforms that profit from this arrangement bear some responsibility — not in law, perhaps, but in their public conduct — to acknowledge what they are doing and to permit the citizen who wishes to see the other paper to find it.

A press that flatters its reader is a press that has stopped doing its work. The remedy is, as ever, the old one: read widely, doubt cheerfully, and beware the medium that grows too convenient.