The lusty cry that roused the Highlanders of ancient Scotland for battle was called a sluagh-gairm. A combination of the Gaelic words for host and cry, this rallying shout became slogorne in English and was over generations altered into sluggorne, slughorn, slogurn and other variants, including slogen. From that came the modern word that embraces those catch phrases, mottoes, aphorisms and partisan whoops that are continually coined and used by every segment of society, from politicians to Boy Scouts to terrorists. Slogans are, in fact, as common as chitchat.
The birth of...