Final answer:
In the sentence "Have a happy birthday," the implied simple subject is 'you,' and the simple predicate is 'Have.' Subject and predicate must agree in number, and simple sentences may have an implied subject.
Step-by-step explanation:
In the sentence “Have a happy birthday,” the simple subject is the implied pronoun “you,” as the sentence is in the form of a command, and in English, the subject of a command is typically the person being spoken to, implied, and thus omitted. The simple predicate, or verb, in this sentence is “Have.”
When analyzing sentences to identify their elements, it is important to remember that a subject names something and the predicate contains the verb, which expresses an action, an occurrence, or a state of being. Verb and subject agreement are key, with singular subjects requiring singular verbs and plural subjects requiring plural verbs. Sentences can be simple with a single independent clause, and in some cases, the subject is implied rather than explicitly stated.