It’s a perpetual lament: The purity of the English language is under assault. These days we are told that our ever-texting teenagers can’t express themselves in grammatical sentences. The media delight in publicizing ostensibly incorrect usage. A few weeks ago, pundits and columnists lauded a Wikipedia editor in San Jose, Calif., who had rooted out and changed no fewer than 47,000 instances where contributors to the online encyclopedia had written “comprised of” rather than “composed of.” Does anyone doubt that our mother tongue is in deep decline?

Well,...