a main idea, a thesis statement, or a claim
You may be thinking of the 'subject'.
Let's see. An incomplete sentence is. As we continuing looking for the definition of an incomplete sentence, we will. No, that direction will only. I keep trying to think of an answer but have. I...
compacted..
"Be punctual" is a complete sentence, because the verb is in the imperative mood, in which the subject "You" is always implied by the verb itself.