The sentence

‘I know him to be an honest man’
We can use that or a to-infinitive after these verbs to refer to people or things:
believe, consider, discover, find, imagine, know, prove, suppose, think, understand.
Instead of: People know (that) he is and honest man.
We can say: People know him to be an honest man.
‘I agreed to accept their offer’
We can use that or a to-infinitive after these verbs:
agree, arrange, claim, choose, decide, expect, hope, pretend, promise, swear, threaten, wish.
Instead of: I agreed that I would accept their offer.
We can say: I agreed to accept their offer.
D. Adjectives and nouns + to-infinitive
Adjective + ‘to’: ‘It was kind (of him) to help us’
We can use a to-infinitive after adjectives in a variety of ways, for example:
1. We use a personal subject (he, she, etc.), or we use it with adjectives like these:
clever, foolish, generous, good, polite, right/wrong, rude, selfish, silly, wicked.
Instead of: He was kind (enough) to help us. She was silly not to buy it.
We can say: It was kind (of him) to help us. It was silly (of her) not to buy it.
We can also say: He was so good/kind (etc.) as to help us.
2. We use only a personal subject (he, she, it or name) with these adjectives:
afraid, anxious, ashamed, careful, curious, eager, fit, free, frightened, glad, keen, sorry:
John is eager to please. (Not *It is eager to*) I’m sorry to have troubled you.
3. We use a personal subject or it, but not of him, etc. with these adjectives:
agreeable, amusing, boring, difficult, easy, hard, impossible:
John is easy to please. It is easy to please John.
Adjectives with ‘too/enough’: ‘too weak/not strong enough to’
1. Too before an adjective means ‘excessively’:
He isn’t strong. He can’t lift it. → He is too weak to lift it. (Not *very weak to*)
2. Enough after an adjective means ‘to the necessary degree’. It combines two ideas:
He is strong. He can lift it. → He’s strong enough to lift it.
He is weak. He can’t lift it. → He isn’t strong enough to lift it.
Noun + to-infinitive: ‘My decision to wait was wise’
1. Some nouns are related to verbs which are followed by a to-infinitive.
They may have a different form from the verb: I decide to → it’s my decision to;
or they may have the same form as the verb: I wish to → it’s my wish to.
2. Some nouns are related to adjectives which are followed by a to-infinitive.
They usually have a different form from the adjective:
I am determined to → my determination to; I am eager to → my eagerness to.
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