Imperative vs. Declarative (can a third grader or his parents tell the difference?)
Solution 1:
No, it is not in the imperative. An imperative verb almost never has a subject. These are imperative sentences:
- Go to the store.
- Michael, go to the store.
- You give me that right now.
These are all declarative sentences:
- You are going to the store.
- You will go to the store.
- You might go to the store.
- You should go to the store.
- You have to go to the store.
- You ought to go to the store.
- You shall go to the store.
- You must go to the store.
How you want to classify this one, however, may vary:
- Let's go to the store.
Solution 2:
"Join with the giants" is in the imperative mood. (It's a direct command. It has an implied subject of "you," but the subject itself is not stated.)
"You must join with the giants" in the declarative mood because it expresses a fact not a command. For example, you could say "You must join with the giants if you're going to fight the dragons."
The confusion arises from the usage of the deontic modal "must." Because a deontic modal implies the way the world ought to be rather than the way the world is, it is a statement of belief about what needs to be changed. It is not, however, an explicit command to change anything.
For your third grader, it's probably fine just to say that it's an imperative because it's saying you have to do something. Let him learn the subtler linguistic distinction when he's older. For now, meaning matters more than syntax.
Solution 3:
This is all about terminology. As the others have said, on a syntactic level, it is in the indicative mood (not imperative); on a semantic/illocutionary level, it is a directive (not an assertive, declarative, interrogative, or expressive). The term imperative is usually restricted to the syntactic mood, so you should probably be looking at that; then your son's sentence is indicative.
The other terms, however, make one think of illocutionary functions. The opposition imperative v. declarative makes it seem as though his teacher were confusing semantics with syntax or were just generally imprecise. In that case, it's anybody's guess what she meant. See Speech Acts and Moods.
Solution 4:
I've come across the following at http://voices.yahoo.com/four-kinds-sentences-declarative-interrogative-484238.html?cat=4 :
Four Kinds of Sentences: Declarative, Interrogative, Imperative and Exclamatory
... The best way to distinguish one sentence from the other is to memorize what each type of sentence does, for instance you can say, declarative sentences are the statement sentences, interrogative sentences are the question sentences, imperative sentences are the request and command sentences, or the giving order sentences, and exclamatory sentences are the ones that show a strong feeling or emotion. ...
I agree with the portion I've bolded, but buying into the above passage can be shown to lead to the contradictions we're discussing:
This analysis possibly identifies "You must join with the giants." (or certainly "You must join with the giants!" as a 'command sentence'. The 'what each type of sentence does' analysis thus cuts across the prescriptive syntax-based 'Declarative, Interrogative, Imperative and Exclamatory' analysis - which I believe John Lawler is saying is 'not a model of the English language' - as Cerberus has stated.