Punjab, Oct. 10 -- On Saturday the Indian state prevented a protest in its capital by detaining four former Chief Ministers and shutting fifty-seven Metro stations. Nobody has been charged with anything. Preventive detention was not designed for this, and using it this way costs more than the protest would have.

What the power is actually for

Preventive detention in ordinary policing - as distinct from the special statutes - rests on a specific logic: an officer who has concrete reason to believe a named person is about to commit a cognisable offence may detain them to stop it. The test is anticipation of a particular breach by a particular person.

It is not a crowd-management tool. The moment it is applied to everyone who might attend a...