To begin, he and colleagues fed the computer 80 sarcastic sentences and several hundred non-sarcastic sentences that they had plucked from Amazon user reviews.

That rise had several causes, among them the greater number of people imprisoned for non-violent crimes and the heavier sentences that came with new laws laying down mandatory minimum terms.

Non-custodial community sentences have yet to prove their worth; the rate of recidivism seems disappointingly close to that of people who serve prison terms.