關於愛，我是個小學生。

In English, there are three “moods.” A mood is a way of using a verb to show the attitude of the speaker toward what he is saying. The Indicative mood expresses facts. All the tenses discussed in the Grammar Corner, Verb Tense section are in the indicative mood. The other two moods are the imperative mood and the subjunctive moods.
It is important to remember that there are only a few acceptable situations to use the command form in, such as talking to children, to your students, when giving instructions, etc. Otherwise, it is more polite to request people to do things, using modals such as “would,” “could,” “will” and “can”:

“Could you give me a wrench, please?”
“Will you please clean your room?”
“Would you read this report, then give it to your supervisor?”
“Can you send us your e-mail address?”

The subjunctive mood is used to express emotion, doubt, desire and possibility. It has mostly disappeared in English, though it is very important in other European languages. Even educated speakers of English do not regularly use the subjunctive correctly.

“If I were (not “was”) a rich man, I'd travel all over the world.”
“If she were (not “was”) any taller, she'd be taller than her husband.”
The subjunctive also occurs in clauses with the verb “wish”:
“I wish I were (not “was”) in California.”

The subjunctive mood is used in object complements where the verb in the main clause is a verb like “suggest,” “recommend,” “demand,” “ask,” etc.:

“I suggest that he take (not “takes”) the day off.”
“I demand that all employees be (not “are”) here on time.”
“They asked that we sing in the choir.” (“Sing” has the same form in the subjunctive as it is in the indicative mood. Most verbs in the subjunctive mood are only recognizable in the third person singular. “We” is first person plural. “Be” is the only exception.)

The subjunctive mood is also expressed in sentences beginning with “It is important that...”:

“It is important that you be (not “are”) ready for an emergency.”
“It is very important that I be (not “am”) prepared for the presentation.”

Finally, the subjunctive mood is still used in established or idiomatic expressions, such as “(May) God bless you,” “So be it,” “(May) God be with you,” etc.

There are two “voices”: the active voice and the passive voice. The active voice sentence is the typical English sentence:
SUBJECT + VERB + OBJECT.

The structure of a sentence in the simple passive voice is different:
OBJECT + be/get + PAST PARTICIPLE (+ AGENT).

The active voice is used in most conversational situations. The passive voice is used in explanations, such as this one, where the object (“the passive voice”) is more important than the people who use it. The passive voice is also used a lot in reporting where the agent is unknown, unimportant or purposely kept secret. For example, the following sentences have no agent:

“Bananas are grown in Ecuador.” (The object, “bananas,” is more important than who grows the bananas. We probably don't know who grows the bananas anyway.)
“The diamond was stolen at 4:30a.m.” (We don't know who stole the diamond, so no agent can be included. Even if we did know, the sentence might still be more common in the passive because the fact that a diamond was stolen may be more important than who did it.)

As stated above, “get” is sometimes used in conjunction with the past participle when forming the simple passive voice. Using “get” is a more casual way of making the passive voice. “Get” tends to emphasize the feelings of the speaker as well as process, whereas “be” emphasizes neutrality and state of being. “Get” doesn't take an agent as often as “be” does.


~ adapted and rearranged from "riverso"