Mark Twain passage of boat, was a measure on the sounding line. Twain is an archaic term for "two", as in "The veil of the temple was rent in twain." The riverboatman's cry was "mark twain" or, more fully, "by the mark twain", meaning "according to the mark [on the line], [the depth is] two [fathoms]", that is, "The water is deep and it is safe to pass." Twain said that his famous pen name was not entirely his invention. In "Life on the Mississippi", he wrote: Captain Isaiah Sellers was not of literary turn or capacity, but he used to jot
Old English grammar known as "ablaut". In this form of conjugation, the stem of the word changes to indicate the tense. Verbs like this persist in modern English; for example "sing, sang, sung" is a strong verb, as are "swim, swam, swum" and "choose, chose, chosen". The root portion of the word changes rather than its ending. In Old English, there were seven major classes of strong verb; each class has its own pattern of stem changes. Learning these is often a challenge for students of the language, though English speakers may see connections between the old verb classes and their modern forms.