3.13 Adjectives not allowing modification by passive infinitives

Examples of errors:

1. Good relationships are difficult to be established.
2. That's what makes such problems so hard to be solved.

Quirk et al. (1972:§12.38-43) distinguish five types of adjectives that can be modified by an infinitive clause, according to various paraphrase relations and semantic criteria. Type I adjectives can be paraphrased by sentences with it, e.g.:

John is splendid/wonderful/clever/foolish to run for office
= It is splendid/wonderful/clever/foolish of John to run for office

In Type II the subject of the main verb (be) is the object of the infinitive, e.g.:

John is hard/easy/difficult to know.
= It is hard/easy/difficult to know John.

Some adjectives of this type do not have equivalent it constructions:

The air is frosty to breathe.
*It is frosty to breathe the air.

The food is ready to eat.
*It is ready to eat the food.

The paper is flimsy to write on.
*It is flimsy to write on the paper.

Type III adjectives have adverbial paraphrases:

John was prompt/quick/slow to react.
= John reacted promptly quickly slowly.

Type IV adjectives are attitudinal expressions, where "the relation of the infinitive clause to the rest of the sentence is that of a quasi-agent expressing cause" (Quirk et al. 1972:§12.42), e.g.:

John was angry/glad/disgusted/impatient/surprised to hear about it.
= Hearing about it angered/disgusted/surprised John/made John impatient

Type V adjectives express volition--the intention or willingness either to do something or not to do it, e.g.:

John was hesitant/prone/reluctant/willing/inclined/disposed to run for office

Most of the adjectives that allow a passive infinitive belong to Type IV and V. e.g.:

John was angry/content/glad/impatient/astonished/reluctant/to be elected

Type I-III adjectives do not generally allow passive infinitives, e.g..:

*John was difficult/foolish/wonderful/easy/convenient to be elected
*The air is frosty to be breathed.
*The paper is flimsy to be written on.

Compare, however:

John was slow/quick to be elected.
You were foolish to be talked into it.

In the last example, to be talked into may be considered elliptical for to let yourself be talked into, in which case the main verb (let) in the infinitive clause is active. Ready in some cases allows both the active and passive infinitive, with no difference in meaning, e.g.:

The food is ready to eat/be eaten