Possible Duplicate:
Shortest complete sentence in English
I seem to remember (back in the day) being taught sentences must have an object and an action and that the shortest possible was something like "do it.".
Can someone please formalise this and explain whether simply "no." is valid?
Yes.
Single-word sentences are fine, because subjects and predicates can be implied.
If we were driving in a car, and you kept singing an annoying ad jingle over and over again, I might say, "Stop!"
"Stop!" is a one-word sentence. The subject (you) is implied. It's essentially a shortened version of, "Will you please stop singing that song!"
Contextually, it would be obvious that I was asking you to stop, not the car. It would be obvious that I was asking you to stop singing, not stop breathing. Hence, I don't need to add those words, just to make it a sentence. I simply yell, "Stop!" and you figure out the rest.
