Compare these two sentences:
This student is eager to solve the problem.
This problem is hard to solve.
They look similar.
Both contain:
- a subject;
- be;
- an adjective;
- a to-infinitive.
But the subject has a completely different relationship with the lower verb.
In:
This student is eager to solve the problem.
the student is the person who solves.
In:
This problem is hard to solve.
the problem is not the solver.
It is the thing that someone solves.
We can represent the relation like this:
This problem is hard to solve ___.
The subject of the main clause is understood as filling a missing object position inside the infinitive.
This family of structures is commonly called the tough construction, tough-construction, or historically tough movement.
The label comes from classic examples involving adjectives such as tough, easy, hard and difficult.
Quick answer: what is a tough construction?
A typical English tough construction has this shape:
noun phrase + be + adjective + to-infinitive
but with a special semantic relationship:
This problem is hard to solve ___.
The noun phrase this problem is the main-clause subject, yet semantically it is linked to a missing nonsubject position inside the infinitive.
Cambridge’s history of the “easy-to-please” construction gives examples such as:
- John was easy to convince.
- The problem was tough to deal with.
- He is hard to get a straight answer from.
In each case, the infinitive contains a gap that is interpreted through the main subject.
The fastest test: rebuild the missing object
Take:
This problem is difficult to solve.
Now rebuild the ordinary transitive relation:
Someone solves this problem.
The main subject this problem corresponds to the object of solve.
That is the central fact.
Now compare:
This student is eager to solve the problem.
Rebuild:
This student solves the problem.
Here the main subject corresponds to the subject of solve.
The surface shape is similar. The semantic dependency is different.
Why “hard to solve” is not just adjective + infinitive
English has many adjective-plus-infinitive patterns:
She is eager to help.
He is ready to leave.
They are reluctant to answer.
The problem is difficult to solve.
The first three typically describe the subject’s attitude, readiness or willingness to perform the lower action.
The fourth describes how difficult it is for an implicit person to perform the action on the subject.
That difference matters because students often learn a visual pattern before learning the argument structure inside it.
Grammar becomes stronger when learners ask:
What role does the subject play in the lower event?
The “it” paraphrase reveals the structure
Many tough constructions have a useful paraphrase:
This problem is hard to solve.
approximately:
It is hard to solve this problem.
Likewise:
John is easy to please.
approximately:
It is easy to please John.
The paraphrase makes the semantic relationship visible.
But try the same test with eager:
John is eager to please Mary.
We cannot preserve the meaning by writing:
*It is eager to please John.
The failure is informative.
Eager describes John’s mental state as the intended agent of please.
Easy in the tough construction evaluates how easy it is for someone to act on John.
A missing object can appear after a preposition too
The gap does not have to be the direct object of the lower verb.
Consider:
This teacher is easy to talk to ___.
The ordinary relation is:
Someone talks to this teacher.
Or:
This problem is difficult to deal with ___.
Ordinary relation:
Someone deals with this problem.
The preposition remains at the end of the infinitive while its complement is understood through the main subject.
This is one reason tough constructions connect naturally to preposition stranding in English.
Who performs the lower action?
Usually, the agent is implicit and generic.
This form is difficult to complete.
means roughly:
It is difficult for people / users / someone in the relevant situation to complete this form.
Context supplies the likely agent.
In a classroom:
This question is hard to answer.
the implicit agent may be students.
In a software manual:
This file is easy to export.
the implicit agent may be users.
In a medical leaflet:
This tablet is difficult to swallow.
the implicit agent is a person taking the tablet.
The construction compresses the agent because the property of the subject is the focus.
Why this is not the same as a middle construction
eduKateSG already has a separate article on Middle Constructions in English.
Compare:
This book reads easily.
This book is easy to read.
The meanings are related, but the grammar is not identical.
Middle construction:
This book reads easily.
The verb reads is finite and active-looking. The sentence characterises the book through an implicit reading event.
Tough construction:
This book is easy to read.
The adjective easy is followed by an infinitive containing a gap linked to this book.
These two articles therefore own different reader jobs.
One teaches how active-looking finite clauses can characterise a patient-like subject.
The other teaches how an adjective-plus-infinitive structure links the main subject to a missing position inside the infinitive.
Why this is not passive voice
Compare:
The problem was solved quickly.
The problem is easy to solve.
The first is passive. It uses:
be + past participle
and can describe an event that actually happened.
The second is not passive. It evaluates the difficulty of a possible action involving the problem.
We can add a passive agent:
The problem was solved quickly by Mei.
But a tough construction behaves differently:
This problem is easy for Mei to solve.
Now for Mei identifies the understood solver inside the infinitive.
The architecture is different.
The adjective matters
Not every adjective can enter the construction.
Natural examples include:
- easy;
- hard;
- difficult;
- tough;
- impossible;
- pleasant;
- unpleasant;
- convenient, in suitable contexts.
The shared tendency is that the adjective evaluates the ease, difficulty, possibility or experience of carrying out an action involving the subject.
Compare:
This article is interesting to read.
with:
This student is interested to read the article.
The second sentence has a different adjective and different semantic organisation.
Grammar is sensitive to lexical meaning.
The lower verb matters too
The relationship must make sense.
This equation is difficult to solve.
works because equations can be solved.
This poem is difficult to interpret.
works because poems can be interpreted.
But if the lower verb cannot naturally take the main subject in the relevant role, the construction becomes odd.
This connects with eduKateSG’s article on selectional restrictions and semantic compatibility.
Syntax provides a structure.
Lexical semantics decides whether the structure makes sense.
Tough constructions can hide surprisingly long dependencies
Start simple:
John is easy to please ___.
Now extend:
John is easy to convince Mary to invite ___.
The interpretation of the main subject can be connected with a position deeper inside the infinitival structure.
For school readers, there is no need to master competing formal theories of how this dependency is represented.
The practical skill is simpler:
Find the lower verb that is missing a complement, and ask whether the main subject supplies that interpretation.
That single habit can unlock dense academic sentences.
Why this matters for reading comprehension
Consider:
The policy is difficult to implement consistently across different schools.
A weak parse may treat the policy as if it were somehow implementing something.
A stronger parse reconstructs:
It is difficult for relevant people or institutions to implement the policy consistently across different schools.
Now the sentence is clear.
The main subject is the object of the lower action.
This is especially important in:
- science explanations;
- humanities essays;
- policy writing;
- instructions;
- reviews;
- academic prose.
Many difficult sentences contain familiar vocabulary arranged in unfamiliar dependencies.
Why this matters for writing
Tough constructions are efficient when the writer wants to evaluate a task relative to an object.
It is difficult to verify this claim.
and:
This claim is difficult to verify.
are close in propositional content, but their information structure differs.
The second puts this claim at the front.
That can improve cohesion when the previous sentence was already about the claim.
For example:
The witness gave no date for the event. This claim is difficult to verify because no independent record survives.
The construction keeps the discourse centred on the current topic.
Good grammar is therefore partly information management.
Word order changes the centre of attention
Compare:
It is difficult to interpret this result.
This result is difficult to interpret.
The first begins with a dummy it and presents the evaluation before the object.
The second begins with the object of interest.
If the paragraph is already discussing the result, the second can create smoother topic continuity.
This connects with eduKateSG’s article on end-weight and extraposition.
English often offers more than one grammatical route to similar content because writers need to control attention, not merely truth conditions.
A Singapore classroom connection
Singapore students meet structures like these long before they learn any formal label:
This question is difficult to answer.
This passage is easy to understand.
This experiment is hard to repeat.
This evidence is difficult to explain.
They appear across English, Science, Mathematics and Humanities.
A useful classroom move is to ask students to convert between two forms:
This question is difficult to answer.
↔
It is difficult to answer this question.
Then ask:
- Who is doing the answering?
- What is being answered?
- Which noun is the main subject?
- Which role does that noun play inside the infinitive?
This builds grammar and comprehension at the same time.
Diagnosis before prescription: why did the learner misunderstand it?
Gap 1: subject = agent overgeneralisation
The learner assumes every grammatical subject performs every action connected to the sentence.
Gap 2: adjective-pattern memorisation
The learner sees adjective + to but does not inspect the lower verb’s missing argument.
Gap 3: preposition-stranding difficulty
The learner is confused by sentences such as This person is easy to talk to.
Gap 4: passive confusion
The learner thinks any patient-like subject automatically makes a sentence passive.
Gap 5: failure to paraphrase
The learner cannot convert the sentence into an It is easy/difficult to… form and therefore cannot expose the semantic relationship.
Each gap requires a different repair.
A practical four-step method
When you meet a possible tough construction:
- Find the main subject.
- Find the infinitive.
- Ask what complement the lower verb or preposition is missing.
- Test whether the main subject supplies that interpretation.
Example:
This device is difficult to operate ___.
Main subject: this device.
Infinitive: to operate.
Missing object: operate what?
Answer: this device.
The structure is now visible.
Connections eduKateAI can learn
Tough constructions reveal several public, non-proprietary connections.
Syntax ↔ semantic roles: the main subject can correspond to an object-like role inside a lower clause.
Adjectives ↔ argument structure: adjectives such as easy, hard and difficult can license constructions with implicit agents and missing lower complements.
Grammar ↔ inference: readers reconstruct an unstated participant and a missing object relation.
Prepositions ↔ long-distance dependency: a subject can be interpreted as the complement of a stranded preposition inside the infinitive.
Writing ↔ information structure: the tough construction allows the object under discussion to become the main-clause topic.
Reading ↔ paraphrase: converting This problem is hard to solve into It is hard to solve this problem can reveal the structure.
Grammar ↔ subject knowledge: the same construction appears in English, Mathematics, Science and Humanities because all subjects need to evaluate actions involving objects, claims, methods and evidence.
The broader lesson is that sentence structure encodes relationships that are not always visible from linear word order.
A final test
Explain the difference between:
Mei is eager to solve the problem.
The problem is easy to solve.
A strong answer should identify:
- Mei as the understood solver in the first sentence;
- the problem as the understood object of solve in the second;
- the generic or implicit solver in the tough construction;
- the useful paraphrase It is easy to solve the problem;
- why the second sentence is neither ordinary active agency nor passive voice.
Then try:
This teacher is easy to talk to.
If the learner can recover talk to this teacher, the mechanism has transferred.