Read the following sentences carefully:

1. I play tennis every day.
2. We played a match yesterday.
3. They will play with us tomorrow.

In sentence 1, the verb play refers to present time.
In sentence 2, the verb played refers to past time.
In sentence 3, the verb will play refers to future time.
Thus verb may refer to

1. Present Time
2. Past Time  or
3. Future Time.

Since three main time divisions are: present, past and future, they may be represented by three main blocks of tenses:

1. The Present Tense
2. The Past Tense
3. The Future Tense

Depending on the interest and attitude of the speaker indicated by them, tenses are divided as

1. indefinite or simple,
2. continuous or progressive,
3. perfect, and
4. perfect continuous.

This classification takes into account both form and function.
These four sub-divisions of each tense clearly indicate the stage of action:
e.g.

1. The Simple form simply states am action. It does not say anything about the completion of the action—whether it is complete or not.
2. The Continuous form indicates that the action is in progress. It is still going on.
3. The Perfect form indicates that the action has been completed.
4. The Perfect Continuous form shows that the action which began sometime before, is still in progress.

Thus, the tense of a verb shows not only the time of an action or event, but also the state of an action.
In other words, we may say that tense is the form of a verb which shows the time at which an event occurs and the degree of completeness / incompleteness of the event.
Read the following sentences:

1. I write a letter    (Simple Present)
2. I am writing a letter.    (Present Continuous)
3. I have written a letter.    (Present Perfect)
4. I have been writing a letter since 7 a.m.    (Present Perfect Continuous)

The verbs in the above sentences refer to present time. Therefore, these sentences are in the present tense.
The Past Tense also has the following four forms:

1.    I wrote a letter yesterday.    (Simple Past)
2.    I was writing a letter at that moment.    (Past Continuous)
3.    I had written before you came.    (Past Perfect)
4.    I had been writing letters all day yesterday.    (Past Perfect Continuous)

Similarly, the Future Tense has the following four forms:

1. I shall write to you tomorrow.    (Simple Future)
2. I shall be writing on reaching home.    (Future Continuous)
3. I shall have written a letter by evening.    (Future Perfect Tense)
4. I shall have been writing for an hour before you arrive. (Future Perfect Continuous)

Now study, the following tense chart giving the forms of the verb ‘write’:

TENSE CHART

Tense	Simple	Continuous	Perfect	Perfect Continuous
Present	write writes	am writing is writing are writing	has written have written	has been writing have been writing
Past	wrote	was writing were writing	had written	had been writing
Future	shall write will write	shall be writing will be writing	shall have written will have written	shall have been writing will have been writing