Did Shakespeare commit mistakes in his use of English ?
Difference between Shakespeare's English and Modern English.
Language must have changed in the course of a long time. Elizabethan English shows the style of old English. I.E. inflected English had case-ending for the nouns, terminations for the verbs, and the like. by the end of the 16th century, most of these inflections had ended, though some remained as it is, and the influence of the earlier inflected stage still affected the language. often when we interrogate into the history of some Elizabethan idioms which seem to us curious we find that it is a relic of an old usage.
there are numerous cases in the poet's works where a verb in the present tense has the inflection- s, though the subject is plural: cf the following lines in Richard II,