I'm happy.
I'm happy too.
I'm not happy.
I'm not happy either.
We use too and either at the end of a sentence.
too after a positive verb:
• A: I'm happy.
B: I'm happy too.
• A: I enjoyed the film.
B: I enjoyed it too.
• Mary is a doctor. Her husband is a doctor too.
either after a negative verb:
• A: I'm not happy.
B: I'm not happy either. (not 'I'm not ... too')
• A: I can't cook.
B: I can't either. (not 'I can't too')
• Bill doesn't watch TV. He doesn't read newspapers either.
I'm happy.
So am I.
I'm not happy.
Neither am I.
so am I = I am too
so have I = I have too (etc.)
• A: I'm working.
B: So am I. (= I'm working too)
• A: I was late for work today.
B: So was John. (= John was late too)
• A: I work in a bank.
B: So do I.
• A: We went to the cinema last night.
B: Did you? So did we.
• A: I'd like to go to Australia.
B: So would I.
neither am I = I'm not either
neither can I = I can't either (etc.)
• A: I haven't got a key.
B: Neither have I. (= I haven't either)
• A: Ann can't cook.
B: Neither can Tom. (= Tom can't either)
• A: I won't (= will not) be here tomorrow.
B: Neither will I.
• A: I never go to the cinema.
B: Neither do I.
You can also use Nor ... (= Neither ...):
• A: I'm not married.
B: Nor am I. or Neither am I.
Note that we say: So am I (not 'So I am'). Neither have I (not 'Neither I have').
I am / I don't etc. → UNIT 39