The decision, handed down this week, that a citizen's individual data may not be incorporated into the training of an artificial intelligence without affirmative consent, is being treated in some technical quarters as an obstacle to progress. I would treat it differently. It is, more accurately, the restoration of an old principle to a new instrument.

The principle is that the right to be left alone — to keep one's affairs private from the systematic gaze of any institution, public or private — is the foundation on which all the other rights of a free citizen are built. A people surveilled is a people whose other liberties are conditional. A people whose every communication, every transaction, every movement is logged and retrieved is a people who has, by quiet accumulation, ceded the moral independence that makes citizenship meaningful.

The ruling does not, as some commentators have suggested, render the artificial intelligence unworkable. It does not require companies to forget what they have learned in the aggregate; the broad statistical regularities by which language is modelled, the prices by which markets clear, the patterns by which diseases progress — these are not the citizen's individual record, and the firm may continue to learn from them. What the ruling requires is the simpler and older thing: that when the firm wishes to incorporate the citizen's individual communications, individual transactions, individual movements, it must ask.

A free people may consent to be read in the aggregate; they have always required consent to be read by name. The technological argument that distinguishing one from the other is difficult is precisely the argument I am least sympathetic to. The firm whose business model depends on the harvest of individual records without consent has built its business on a foundation the Constitution does not protect. That foundation may have to be rebuilt. The Republic will be the better for the rebuilding.

I am told that the firms most affected have warned of harms — innovations not delivered, services not improved, costs not lowered. I do not doubt the warnings are sincere. I would simply observe that every restraint on power has historically been met with the same warning, from the merchant who could not adulterate his goods to the printer who could not libel his rival. The warnings prove out, in most cases, less than the warners expect; the warned-against innovations prove out, in most cases, better than the warned-against expect.

The right of the citizen to refuse the algorithm's notebook is the precondition of citizenship in any age. The Court restored that right today. The Republic is the safer for it.