1. The Japanese imperfect verbal form ending is -u after consonantal stems, and -ru after vowel stems;
a. This form is called by some grammars the "present tense" (Shibatani 1996: "conclusive/attributive") because it indicates that an action has not been successfully completed; this is the classic definition of the imperfective.
b. The alternate form, -ru, is the result of a shortening of áru, "be at, exist", in its imperfective form.
c. Japanese -u is the residue of a reduction of -*wa, which represents PL F/F[H]A.
d. Exx.: Ano ko wa yoku hon o yomu, "that child reads well"; sonna hon wa yomu na, "do not read such (a) book(s)!"