2-1 Simple Present
(past) -x-x-x-x-x- + -x-x-x-x-x- (future)
(a) Water consists of hydrogen and oxygen.
(b) The average person breathes 21,600 times a day.
(c) The world is round.
The simple present says that something was true in the past, is true in the present, and will be true in the future. It expresses general statements of fact and general truths.
(d) I get up at seven every morning.
(e) I always eat a salad for lunch.
The simple present is used to express habitual or everyday activities.
2-2 Present Progressive
(past) ---x(start)------ + ------x(finish?)↲--- (future)
(f) The students are sitting at their desks right now.
(g) I need an umbrella because it is raining.
(h) I am talking five courses this semester.
The present progressive expresses an activity that is in progress at the moment of speaking. It is a temporary activity that began in the past, is continuing at present, and will probably end at some point in the future.
2-7 Simple Past
(past) ---x--- + ------ (future)
(a) I walked to school yesterday.
(b) John lived in Paris for ten years, but now he lives in Rome.
(c) 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.
(d) Rita stood under a tree when it began to rain.
(e) When Mrs. Chu heard a strange noise, she got up to investigate.
(f) When I dropped my cup, the coffee spilled on my lap.
If a sentence contains when and has the simple past in both clauses, the action in the when-clause happens first.
In (d): 1st: The rain began. 2nd: Rita stood under a tree.
2-8 Past Progressive
(past) ---x(start)---X---x(finish)↲--- + ------ (future)
(g) I was walking down the street when it began to rain.
(h) While I was walking down the street, it began to rain.
(i) Rita was standing under a tree when it began to rain.
(j) At eight o'clock last night, I was studying.
In (g): 1st: I was walking down the street. 2nd: It began to rain.
Both actions occurred at the same time, but one action began earlier and was in progress when the other action occurred.
In (j): My studying began before 9:00, was in progress at that time, and probably continued.
(k) While I was studying in one room of our apartment, my roommate was having a party in the other room.
Sometimes the past progressive is used in both parts of a sentence when two actions are in progress simultaneously.
2-9 Using Progressive Verbs with Always
(a) Mary always leaves for school at 7:45.
In sentences referring to present time, usually the simple present is used with always to describe habitual or everyday activities, as in (a).
(b) Mary is always leaving her dirty socks on the floor for me to pick up! Who does she think I am? Her maid?
In special circumstance, a speaker may use the present progressive with always to express annoyance, as in (b).
(c) I am always/forever/constantly picking up Mary's dirty socks!
In addition to always, the words forever and constantly are used with progressive verbs to express annoyance.
2-10 Using Expressions of Place with Progressive Verbs
(a) What is Kay doing?
-> She is studying in her room.
In usual word order, an expression of place follows a verb.
In (a): is studying + in her room = the focus is on Kay's activity.
(b) Where's Kay?
-> She is in her room studying.
An expression of place can sometimes come between the auxiliary be and the -ing verb in a progressive verb form.
In (b): was + in her room + studying = the focus is on Kay's location.