The English Verb Tenses: Formation and Uses

I. Simple Tenses:
1. Present Tense: (in the 3rd person, the -s form is used; otherwise, use the base form)
 a. It can be used to refer to actions which occur at regular intervals.
 b. It is used in stating general truths or facts.
 c. It is used when referring to printed material, and when describing events portrayed in a book, film, or other literary work.
 d. Occasionally, the Simple Present is used to express actions occurring in the future (must be used with modifiers) or the past (vivid narration).
 e. It is sometimes used to express what is happening at the present time but the present progressive is used more frequently in such cases.

2. Past Tense: (past form of the verb)
 a. It is used to express what happened at a specific time in the past.

Note that the present perfect tense can also be used to express past events.
We use the simple past tense when:

• the event is in the past
• the event is completely finished
• we say (or understand) the time and/or place of the event

 b. It is used in narration.

3. Future Tense: (will/shall + base form of a verb)
 a. It is used to state a future action.
Will versus Shall:
*To simply state future actions:
Shall — First Person
Will – Second Person and Third Person
*For commands, consent, wish, willingness, promise, or determination:
Shall– Second Person and Third Person.
Will– First Person
[N.B. The differences between will and shall are sometimes not observed any longer. In fact, shall is now rarely used in American English.]


II. Perfect Tenses:
 The perfect tenses indicate that the action or condition that they express is related to some other action or condition, which is either stated or understood in the sentence.

1.Present Perfect Tense: (have/has + past participle)
 a. It expresses an action that started in the past and still continues in the present. (Indicators: since and for)
 examples:
  I have been ill since yesterday.
  She has traveled sleeplessly for the past few days.
 b. It can be used to state a change or new information.
  I have bought a computer.
  *Connection with the past: I did not have a computer.
  *Connection with the present: Now I have a computer.
 But take note of this: I bought a computer yesterday.
  *In the sentence above, the past action was done at a specific time in the past.
  *Do not use specific time indicators if you want to use the present perfect tense for past actions.

2. Past Perfect Tense: (had + past participle)
 a. It is used to indicate an action or condition that happened before another past action or condition.
 examples:
 *The culprit had already fled when the policemen came.

3. Future Perfect Tense: (shall have/will have + past participle)
 a. It expresses a future action that is expected to be completed before another future time or action.
 examples:
 *We shall have (or will have) been accountants by 2015.
 *You will have reached the classroom before your professor will reach it.
   
III. Progressive Tenses:
 The progressive tenses signify that an action is or was in progress at a given time, expressed or understood. They are also called the Continuous Tenses.
1. Present Progressive:
is + present participle
 a. It expresses what is happening at the present time;
  example:
  *You are studying about the different verb tenses right now.
 b. It expresses an action or condition that is happening around now or something that is in progress.
  example:
  *We are still learning how to become accountants. (We may not be studying Accounting right now, but our learning is in progress.

2. Past Progressive:
was/were + present participle
 a. It expresses what was in progress in a span of time in the past.
 example:
 *I was studying at 10pm last night. (The action was still in progress at 10 pm. It may still continue at 11pm or later.)
  *I studied at 10pm last night. (The action was already completed at 10 pm. It did not continue.)

3. Future Progressive:
will be/shall be + present participle
 a. It expresses an action or condition that will be in progress in the future.
  example:
  They will be having a meeting at 10 o’clock. (The meeting will not start at 10 o’clock [it may start at 8 o'clock] but it will still be in progress at 10 o’clock and it may still continue in the future)
  They will have a meeting at 10 o’clock. (The meeting will start at 10 o’clock.)
  They will have had a meeting at 10 o’clock. (The meeting is expected to be completed before 10 o’clock).

4. Present Perfect Progressive:
have been/has been + present participle
 a. It expresses an action that recently stopped and has an effect in the present.
  example:
  She’s tired because she has been running.
 b. It expresses an action that started in the past and is still continuing up to the present. It is usually denoted by since and for.
  example:
  We have been discussing for fifty minutes.

5. Past Perfect Progressive:
had been + present participle
 a. The past perfect continuous tense is like the past perfect tense, but it expresses longer actions in the past before another action in the past.
  examples:
  She could smell his breath. She knew that he had been drinking.
  She was tired because she had been running.

6. Future Perfect Progressive:
will have been/shall have been + present participle
 a. We use the future perfect continuous tense to talk about a long action before some point in the future.
  example:
  Our president will have been serving us for many years when she steps down next year.