It seems as if the short one is probably the grandson of the tall one because a grandfather can most likely still be considered a father (hence the nameâgrandfather). However, like the riddle mentions, the short one wonât be considered the son, per se.Â
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As for when the phrase âyou isâ would ever be correct, the answer is never. In order for there not to be a subject-verb agreement error, the pronoun âyouâ always needs a plural verb (such as âareâ). And because âisâ is a singular verb, to say âyou isâ is a subject-verb agreement error.