The long and the short of it

Verb conjugation and contraction - in other words; "The short form".

In English we use the short form a lot. We say things like: I'm / you're / didn't etc. instead of I am / you are / did not etc.

We also use these short forms in informal written English. When we write in the short form, we use an apostrophe (') for the missing letter(s).

Forms of the auxiliary verbs to be, to do and to have:-

To be - Simple Present Form

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I am	I'm	I am not	I'm not
He is	He's	He is not	He isn't or He's not
She is	She's	She is not	She isn't or She's not
It is	It's	It is not	It isn't or It's not
You are	You're	You are not	You aren't or You're not
We are	We're	We are not	We aren't or We're not
They are	They're	They are not	They're not

To be - Simple Past Form

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I was	---	I was not	I wasn't
He was		He was not	He wasn't
She was		She was not	She wasn't
It was		It was not	It wasn't
You were		You were not	You weren't
We were		We were not	We weren't
They were		They were not	They weren't

To do - Simple Present Form

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I do	---	I do not	I don't
He does		He does not	He doesn't
She does		She does not	She doesn't
It does		It does not	It doesn't
You do		You do not	You don't
We do		We do not	We don't
They do		They do not	They don't

To do - Simple Past Form

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they did	---	I / he / she / it / you / we / they did not	I / he / she / it / you / we / they didn't

To have - Simple Present Form

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I have	I've	I have not	I haven't or I've not
He has	He's	He has not	He hasn't or He's not
She has	She's	She has not	She hasn't or She's not
It has	It's	It has not	It hasn't or It's not
You have	You've	You have not	You haven't or You've not
We have	We've	We have not	We haven't or We've not
They have	They've	They have not	They haven't or They've not

To have - Simple Past Form

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they had	I'd he'd she'd it'd you'd we'd they'd	I / he / she / it / you / we / they had not	I hadn't or I'd not he hadn't or he'd not she hadn't or she'd not it hadn't or it'd not you hadn't or you'd not we hadn't or we'd not they hadn't or they'd not

The long and short forms of the modal verbs can, could, shall, should, must, will and would

Can

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they can	---	I / he / she/ it / you / we / they cannot	I / he / she / it / you / we / they can't

Could

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they could	---	I / he / she/ it / you / we / they could not	I / he / she / it / you / we / they couldn't

Must

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they must	---	I / he / she/ it / you / we / they must not	I / he / she / it / you / we / they mustn't

Shall

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they shall	---	I / he / she/ it / you / we / they shall not	I / he / she / it / you / we / they shan't

Should

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they should	---	I / he / she / it / you / we / they should not	I / he / she / it / you / we / they shouldn't

Will

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they will	I'll He'll She'll It'll You'll We'll They'll	I / he / she / it / you / we / they will not	I won't or I'll not He won't or He'll not She won't or She'll not It won't or It'll not You won't or You'll not We won't or We'll not They won't or They'll not

Would

Positive Statement		Negative Statement
Long form	Short form	Long form	Short form
I / he / she / it / you / we / they would	I'd He'd She'd It'd* You'd We'd They'd	I / he / she / it / you / we / they would not	I wouldn't or I'd not He wouldn't or He'd not She wouldn't or She'd not It wouldn't or It'd not* You wouldn't or You'd not We wouldn't or We'd not They wouldn't or They'd not
* Not "good" English, but you will hear occasionally.