[Following excerpted from Azar's Understanding and Using English Grammar]

To illustrate the use of the various verb tenses in English, the following chart will be used:

                              now
                               |
                               |
    past ____________________________________________  future
                               |
                               |

	1. Water consists of Hydrogen. 2. Most animals kill only for food. 3. The world is round.	The simple present says something was true in the past, is true in the present, and will be true in the future. It is used for general statement of fact.
	1. I study for two hours every night. 2. My classes begin at nine. 3. He always eats a sandwich for lunch.	The simple present is used for habitual or everyday activity.
	1. I have only a dollar right now. 2. I don't recognize that man. 3. He needs a pen right now.	The simple present is used with verbs which aren't usually used in the progressive (-ing) forms to indicate a situation that exists right now, at the moment of speaking. ***

*** some common examples: hear, taste, smell, see, know, believe, think, understand, recognize, remember, mean, possess, own, have, belong, want, prefer, need, appreciate, love, like, hate, dislike, seem, look, appear.

II. The Present Progressive (am/is/are + base + -ing)

	1. John is sleeping right now. 2. I need an umbrella because it is raining. 3. John and Mary are talking.	The present progressive expresses an activity that is in progress at the moment of speaking. It began in the recent past, is continuing, and will probably end at some future time.
	1. I am taking five courses this semester. 2. John is trying to improve himself. 3. She is writing another book. 4. It is becoming harder to find inexpensive apartment in New York City.	Often the activity is of a general nature: in progress this week, this month, this year, or even a longer period. Sentence 3 means that she is engaged in writing a book during this period, but it does not mean that at the moment of speaking she is at her desk with pen in hand.

III. The Simple Past (base + -ed or irregular form)

	1. I walked to school yesterday. 2. He lived in Paris for ten years. 3. I bought a new car three days ago.	The simple past indicates that an activity or situation began and ended at a particular time in the past.
	1. I stood under a tree when it began to rain. 2. When she heard an odd noise, she got up. 3. When I dropped my cup, my coffee spilled.	If a sentence contains when and uses the simple past in both clauses, the action in the when clause happened first.

IV. The Past Progressive (was/were + base + -ing)

	1. I was walking down the street when it began to rain. 2. While I was walking down the street, it began to rain. 3. I was standing under a tree when it began to rain. 4. At eight o'clock last night, I was studying. 5. Last year at this time, I was going to school.	The past progressive expresses an activity that was in progress when something else occured in the past. In #1, first I was walking then it began to rain. In #1, 2, & 3, one action began earlier and was in progress when the other action occurred. In #4, my studying began before 8:00, was in progress at that time, and probably continued. In #4 & 5 a continuous action has occurred over an extended time in the past.
	1. Last January, while you were trudging through snow, I was lying on the beach. 2. While I was studying, my roomate was having a party.	When two actions progress simultaneously, the past progressive is used in both parts of the sentence.
	1. It rained this morning. 2. It was raining this morning.	Sometimes, the simple past and the past progressive have almost the same meaning.

V. The Present Perfect (have/has + -ed/-en)

	1. They have moved into a new apartment. 2. Have you ever visited Mexico? 3. I have already seen that movie. 4. I have never seen it.	The present perfect expresses the idea that something happened (or never happened) before now, at an unspecified time in the past. The exact time is not important. What is important is that the time is viewed from the present.
	1. We have had four tests so far this semester. 2. I have written my wife a letter every day for the past two weeks. 3. I have met many people since I arrived in June. 4. I have flown on an airplane many times.	The present perfect also expresses the repetition of an activity before now. The exact time of each repetition is not important.
	1. I have been here since 7:00. 2. We have been here for two weeks. 3. I have had this pair of shoes for three years. 4. I have known him for many years.	When used with for or since the present perfect expresses a situation that began in the past and continues to the present. Note: since + a particular time for + a duration of time

VI. The Present Perfect Progressive (have/has + been + base + -ing)

	Right now I am sitting at my desk. 1. I have been sitting here since 9:00. 2. I have been sitting here for 7 hours. 3. You have been studying for five hours. 4. He has been watching television since 9:00 this morning. 5. It has been raining all day.	The present perfect progressive is used to indicate the duration of an activity begun in the past and continuing to the present. In this meaning, it is used with time words such as for, since, all day, all morning, all week.
	1. I have been thinking of changing my major. 2. All the students have been studying hard. 3. John has been doing a lot of work on his thesis.	When the tense is used without any specific mention of time, it expresses a general activity in progress recently.
	1. I have lived here since 1975. I have been living here since 1975. 2. He has worked at the same store for 10 years. He has been working at the same store for 10 years.	With certain verbs (most notably live, work, teach) there is little or no difference in meaning between the present perfect and the present perfect progressive when since or for is used.

VII. The Past Perfect (had + -ed/-en)

1. My parents had already eaten when I got home. 2. Until yesterday, I had never heard about it. 3. The thief simply walked in. Someone had forgotten to lock the door. 4. He had arrived before we got there. 5. He arrived before we got there. 6. After the guests had gone, I went to bed. 7. After the guests went, I went to bed.

The past perfect expresses an activity that was completed before another activity or time in the past. If before or after is used in the sentence, the past perfect is not necessary because the time relationship is already clear. In these cases, the simple past may be used.

VIII. The Past Perfect Progressive (had + been + base + -ing)

	1. The police had been looking for the criminal for 2 years before they caught him. 2. The patient had been waiting in the emergency room for almost an hour before a doctor treated her. 3. Her skin was sunburned because she had been lying in the sun.	The past perfect progressive emphasizes the continuing nature of an activity that was in progress before another activity or time in the past.
	1. When Judy got home, her hair was still wet because she had been swimming. 2. Her eyes were red because she had been crying.	This tense also may express an activity in progress recently before another time or activity in the past.

IX. The Simple Future (will + base form, or be going to + base)

	1. He will finish work 2. He is going to finish his work tomorrow. 3. I will wash the dishes. 4. I am going to wash the dishes.	The simple future is used to express plans or predictions likely to occur.
	1. Bob will come soon. When Bob comes, we will see him. 2. Linda will leave soon. Before she leaves, she is going to finish some work. 3. I will get home at 5:30. After I get home, I will eat dinner. 4. The taxi will arrive in 5 minutes. As soon as it arrives, we will go. 5. They are going to come soon. I will wait here until they come.	The future is often expressed in a conditional statement expressing a time frame in which some action(s) will occur. In such statements the time clause, beginning with words such as when, before, after, as soon as, and until uses the simple present and the main clause uses the simple future.
	1. I will go to bed after I finish my work. 2. I will go to bed after I have finished my work.	Occasionally, the present perfect is used in a time clause. #1 and #2 have the same meaning. In #2, the present perfect tense stresses the completion of the act in the time clause before the other act will occur in the future.

X. The Present Progressive and the Simple Present to Express Future Time.

1. My wife has an appointment with the doctor. She is seeing her next Tuesday. 2. Sam has already made his plans. He is leaving at noon tomorrow. 3. What are you going to do this afternoon? After lunch, I am meeting a friend. We are going shopping.	The present progressive may be used to express future time when the idea of the sentence concerns a planned event or definite intention. The future meaning is indicated by either future time words in the sentence or by the context.
1. The museum opens at 10:00 tomorrow. 2. Classes begin next week. 3. John's plane arrives at 6:05 next Monday.	The simple present can indicate future if the sentence contains future time words such as tomorrow, next week, and in three years.

XI. The Future Progressive (will + be + base + -ing, or be going to be + base + -ing)

	1.I will begin to study at seven. You will come at eight. I will be studying when you come. 2. Right now I am sitting in class. At this same time tomorrow, I will be sitting here again.	The future progressive expresses an activity that is expected to progress at a time in the future when something else will happen.
	1. Don't call me at nine. I am going to be studying at the library.
	1. She will be coming soon. 2. She will come soon.	Sometimes there is little or no difference between the future progressive and the simple future, especially when the events will occur at an indefinite time in the future.

XII. The Future Perfect (will + have + -ed/-en)

1. I will graduate in June. I will see you in July. By the time I see you, I will have graduated. 2. I will have finished my homework by the time I go out tonight.

The future perfect expresses an activity that will be completed before another time or event in the future. Note: as above, the future tense is indicated only in the main clause of the sentence.

XIII. The Future Perfect Progressive (will + have + been + base + -ing)

	1. I will go to bed at 10 P.M. He will get home at midnight. At midnight I will be sleeping. I will have been sleeping for two hours when he gets home.	The future perfect progressive emphasizes the duration of an activity that will be in progress before another time or event in the future.
	1. When Professor Jones retires next month, he will have taught for 45 years. 2. When Professor Jones retires next month, he will have been teaching for 45 years.	Sometimes the future perfect and the future perfect progressive have the same meaning.