It is proposed by Riddles Brain Teasers and other sites that the shortest sentence in the English language is the imperative "Go." This is because the subject of the sentence, "you," is implied. The imperative "Be," is an equal candidate, as it follows similar logic.
The imperative "Go" has an active verb and an implied subject, and is therefore considered a sentence. It is given as a suggestion or command, typically as a response to an earlier statement or question. Some who dispute that "Go" is a complete sentence believe that "I am" is the shortest sentence in English. Riddles.com offers a brain teaser reflecting this view.