why are these ungrammatical?

[Dr. Jamshid Ibrahim]

Originally Posted by susumuya

OH!
'It is not allowed to smoke here' is also ungrammatical??
So, there is quite a lot of restrictions for the use of 'it'...
Is it also because of the abstractness of the adjective?

I am afraid the rules of using “It” as a subject are complex. Here are some:
1. It is used for identification: It is your mother. It’s me
2.. It is used to refer to nothing, everything, all: Everything is Ok. Isn’t it
3. It is used as an empty subject: with expressions of:
Time, weather, temperature, distance or the present situation: It is wonderful. It’s ten O’clock.
He put his feet up on the stove as it was very cold. "It" refers to the weather not the stove
4. as preparatory subject:
If the infinitive/an ing-form is the subject of the sentence: it is helpful to work with you
It is great meeting you
If the subject of a clause is a clause: It is possible that we work in the same room
5. For the sake of emphasis: It was me who helped you
6. "allow" is one of the words which need personal pronoun because the reference is not clear.

[RonBee]

Originally Posted by Dr. Jamshid Ibrahim

I am afraid the rules of using “It” as a subject are complex. Here are some:
1. It is used for identification: It is your mother. It’s me
2.. It is used to refer to nothing, everything, all: Everything is Ok. Isn’t it
3. It is used as an empty subject: with expressions of:
Time, weather, temperature, distance or the present situation: It is wonderful. It’s ten O’clock.
He put his feet up on the stove as it was very cold. "It" refers to the weather not the stove
4. as preparatory subject:
If the infinitive/an ing-form is the subject of the sentence: it is helpful to work with you
It is great meeting you
If the subject of a clause is a clause: It is possible that we work in the same room
5. For the sake of emphasis: It was me who helped you

Excellent!