Conditional Clauses

PRESENT PERFECT TENSE
How do we make the Present Perfect Tense?
The structure of the present perfect tense is:
subject | + | auxiliary verb | + | main verb |
  |   | have |   | past participle |
Here are some examples of the present perfect tense:
  | subject | auxiliary verb |   | main verb |   |
+ | I | have |   | seen | ET. |
+ | You | have |   | eaten | mine. |
- | She | has |not | been | to Rome. |
- | We | have | not | played | football. |
? | Have | you |   | finished? |   |
? | Have | they |   | done | it? |
Contractions with the present perfect tense
When we use the present perfect tense in speaking, we usually contract the subject and auxiliary verb. We also sometimes do this when we write. 
I have | I've |
You have | You've |
He has
She has
Ithas
John has
The car has | He's
She's
It's
John's
The car's |
We have | We've |
They have | They've |
Here are some examples:
* I've finished my work.
* John's seen ET.
* They've gone home.

PAST PERFECT TENSE
How do we make the Past Perfect Tense?
The structure of the past perfect tense is:
subject | + | auxiliary verb HAVE | + | main verb |
| conjugated in simplepast tense | | past participle |
| had | | V3 |
For negative sentences in the past perfect tense, we insert not between the auxiliary verb and main verb. For question sentences, we exchange the subject and auxiliary verb. Look at these example sentences with the past perfect tense:
  | subject | auxiliary verb | | main verb |   |
+ | I | had |   | finished | my work. |
+ | You | had |  | stopped | before me. |
- | She | had | not | gone | to school. |
- | We | had | not | left. |   |
? | Had | you |   | arrived? |   |
? | Had | they |   | eaten | dinner? |
When speaking with the past perfect tense, we often contract the subject and auxiliary verb:
I had | I'd |
you had | you'd |
he had
she had
it had | he'd
she'd
it'd |
we had | we'd |
they had | they'd |PRESENT PERFECT TENSE PROGRESIVE
Lesson Topic: Using The Present Perfect Progressive And The Difference Between The Present Perfect Progressive And The Present Perfect.

Let's say that your friend calls you up and wants to take you out for dinner.  You really don't feel like going because it started to rain early in the morning, and now it is very wet outside.  It is too wet to go out.  Youare afraid of driving when the roads are so wet and slippery.  You do not know the exact time the rain started, but you want to tell your friend that the rain started in the past (in this situation, early in the morning) and is still continuing.  It is still raining.  You would probably say
It has been raining all day, and the streets are too wet to go out now. |
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This grammar is calledthe present perfect progressive.  It is used to say that something started in the past, and it is still happening.  It is often used to answer how long questionswith for and since.  
So, how do you make the present perfect progressive?  Good question!  Here's how you make it:
It | | has | | been | | raining |
subject | + | have or has | + | been | + | verb with -ing |
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Again, the present perfect progressive is used when an activity started in the past and continues until now.  For example, you may ask a college professor you met at a conference, "How long have you been teaching?"  Professor Brown can answer, "I have been teaching for 23 years."
If you read our lesson on...