Infinitive clauses with impersonal it

Infinitive clauses with impersonal it

It (be) Adj + Infinitve Clause  vs. Gerund Clause (be) Adj

INFINITIVE CLAUSE
The expression "It is + adj/noun to" emphasizes information by bringing it to the front of the clause. The subject of an infinitive clause is optionally expressed as [for + noun] or the accusative pronoun [for + pronoun].
MAIN CLAUSE	SUBORD	COMPLEMENT
"IT" IS + ADJ	"FOR" PRN	INFINITIVE CLS
It's difficult	for me	to guess what will happen.
It's hard		to know when a rat will get loose.
It's impossible	for us	to do  this project in 24 hours
It's important		to take a break twice a day.
It's possible	for you	to work on your own project.
It's exciting	for us	to be  here.
It's likely	for it	to get cold in the laboratory.
"IT IS"  + NP	"FOR" PRN	INFINITIVE CLS
It's a good idea (noun)		to put on your lab coat.
It's a pleasure (noun)	for us	to have you here.
It's an honor (noun)	for us	to work in this lab.

GERUND CLAUSE
A similar meaning is expressed with a gerund clause followed by [be] + adj / noun. ¹ However, the clause cannot be restated with a gerund clause when "it" refers to climate or weather.
SUBJECT	PREDICATE
GERUND CLS	"BE" ADJ
Guessing what will happen.	is difficult.
Knowing when a rat will get loose.	is hard.
Doing this project in 24 hours	is impossible.
Taking a break twice a day.	is important
Working on your own project.	is possible.
Being here	is exciting
¹ Getting cold in the laboratory.	is likely.
GERUND CLS	"BE" + NP
Putting on your lab coat	is a good idea.
Having you here	is a pleasure.
Working in this lab	is an honor.

Past tense "It was + adj…"

¹ The clause cannot be restated with a gerund clause when "it" refers to climate or weather.

Also see It as Subject , It Clefts  and It /There Pronouns 

Word Categories: N – Noun; V – Verb; Aux – Auxiliary; Adj – Adjective; Adv – Adverb; P –Preposition; Det –Determiner.

Phrasal Categories: NP – Noun Phrase; VP – Verb Phrase; AdjP – Adjective Phrase; AdvP – Adverb Phrase; PP – Prepositional Phrase; DP – Determinative Phrase.

Clausal Categories: Cls – clause; F – finite clause; NF – nonfinite clause (Ger – gerund; Inf – infinitive; PPart – past participle).

Word Functions: Subj – subject; Pred – predicate/predicator; Comp – complement: elements required by an expression to complete its meaning (DO – direct object; IO – indirect object);  Adjunct – adjunct: elements not required by an expression to complete its meaning (Subord – subordinator; Coord – coordinator); Supl – supplement: a clause or phrase added onto a clause that is not closely related to the central thought or structure of the main clause.

It is [adjective] that… / for you to…

Restating a that-clauses as an infinitive clause

It is adjective that…  / It is adjective for you to…

IT (ADJ) THAT + SUBJUNCTIVE VERB CLAUSE
It's + adj can be followed by that + a clause with should or a subjunctive verb to express a wish, recommendation or suggestion. The subject is mentioned in the clause.
IT (BE) ADJ	THAT	SUBJUNCTIVE CLS
It is important	that	you be careful at all times.
It is a good idea (noun!)	that	Jack close all cages at night.
It is essential	that	it go well.
It's not necessary	that	they work until 3 a.m.
It is rare	that	we wear lab coats.

IT (ADJ) FOR + INFINITIVE CLAUSE
A similar meaning is expressed with It's + adj followed by an infinitive clause.  The subject (doer of the activity) in the infinitive clause can be included [for+ noun / pronoun].
IT (BE) ADJ	FOR PRN	INFINITIVE CLS
It is important	for you	to be careful at all times.
It is a good idea	for Jack	to close all cages at night.
It is essential	for it	to go well.
It's not necessary	for them	work until 3 a.m.
It is rare	for us	to wear lab coats.