Imperative verbs are an exception to the general rule that a grammatically proper sentence in English cannot have an implied subject. (This differs, for example, from Latin, which is generous with implied subjects.)
Thus, there is no issue of distinguishing between the subject and other nouns in a sentence in the imperative mode because there is no explicit subject. The implicit subject is always the second person "you," either singular or plural.
The imperative mode is marked by the absence of an explicit subject and, in the affirmitive, by the bare infinitive (without "to") of the substantive verb or by "do" followed by the bare infinitive of the substantive verb, and, in the negative, by "do not" or "don't" followed by the bare infinitive of the substantive verb.
Correct, affirmative forms of the imperative:
"Come inside" or "Do come inside."
Correct negative forms of the imperative:
"Do not come inside" or "Don't come inside."
Although other modals such as "must," "should," "ought to," or "have to" coupled to an infinitive may have similar meanings to the imperative, they do not introduce an imperative and require an explicit subject.