The vertical lines represent the four leading forms of English—Northern, Midland, Southern, and Kentish—and the names occurring down the course of each are those of writers and works in that form of English at the given date. The thickness of the line shows the comparative literary position of this form of speech at the time: thick indicating a literary language; medium, a literary dialect; thin, a popular dialect or patois; a dotted line shows that this period is unrepresented by specimens. The horizontal lines divide the periods; these (after the first two) refer mainly to the Midland English; in inflectional decay the Northern English was at least a century in advance of the Midland, and the Southern nearly as much behind it.