Where it appears in the exam
What is it?
The perfect infinitive ('to have done') expresses that the infinitive action occurred BEFORE the main verb action. 'She seems to have left' = it seems she left (first she left, then it seems). It is used with reporting verbs in the passive ('is believed to have stolen'), with verbs of appearance ('seems/appears to have done'), and with expressions of judgement ('He was lucky to have survived'). At B2 level, the difficulty is not understanding the concept — it is PRODUCING the complete structure when Cambridge asks for it in Part 4.
Why it matters in the exam
The perfect infinitive is the piece that connects three Part 4 patterns in a single mechanism: passive reporting verbs ('is said to have done'), seem/appear ('seems to have done'), and transformed modal expressions. Without mastering 'to have + PP', you lose points on the most frequent FCE transformation: 'People say he escaped' → 'He is said TO HAVE ESCAPED'. Each Part 4 transformation is worth 2 points — and this pattern appears in nearly every exam.
The cognitive trap
"The instinct: "She seems to leave" (using simple infinitive for a past action)"
Why your brain does this: in most languages, the compound infinitive ('to have left') is formal and infrequent. Your brain defaults to the simple infinitive because everyday speech rarely requires the perfect form. The shortcut feels natural but loses the past reference.
"She seems to have left" / "He is believed to have stolen the painting"
The English rule: 'to have + PP' is the ONLY form to mark anteriority in an infinitive. There is no alternative. 'She seems that she left' DOESN'T EXIST in English. When transforming in Part 4, you MUST use 'to have + PP' — there is no other option. Your brain looks for a shortcut that doesn't exist in English.
Recognition pattern
In the exam, look for the key signal first. The answer follows.
Recognition signals in the exam
"He is said to ___ escaped" → 'have'
"She seems to ___ forgotten her keys" → 'have'
"People say he left" → 'He is said to have left'
"They think she won" → 'She is THOUGHT to have won'
"The castle is thought to ___ been built in 1400" → 'have'
"He was lucky to ___ survived the accident" → 'have'
"She claimed to ___ met the president" → 'have'
Mistakes Cambridge exploits
"She seems to have forgot about the meeting."
After 'to have', you need the past participle (forgotten), not the past simple (forgot). 'Have + forgot' doesn't exist — 'have + forgotten' is the correct form.
"She seems to have forgotten about the meeting."
After 'to have', you need the past participle (forgotten), not the past simple (forgot). 'Have + forgotten' is the correct perfect infinitive form.
"She seems to forget about the meeting."
'Seems to forget' = it seems she forgets habitually. But the context is a specific past event. The 'have' is what marks that the action already occurred.
"She seems to have forgotten about the meeting."
Perfect infinitive: the action (forgetting) occurred before the present moment. 'Seems' is now, 'to have forgotten' is prior.
"The painting is thought to have stolen during the night."
Without 'been', the painting steals — it is not stolen. 'To have stolen' is active: 'The painting stole' (impossible). You need 'to have BEEN stolen' for the passive within the perfect infinitive.
"The painting is thought to have been stolen during the night."
PASSIVE perfect infinitive: to have been + PP. Double layer: 'to have' (anteriority) + 'been stolen' (passive). The painting was stolen (passive) before the moment of thinking.
"He claimed to visit over 50 countries."
'Claimed to visit' = he claimed he would visit or visits habitually. But the context says he ALREADY visited. The simple infinitive loses the past reference.
"He claimed to have visited over 50 countries."
Perfect infinitive after 'claim': the action (visiting) is prior to the declaration (claiming). He visited first, then claims.
"You were supposed to finish by now."
Grammatically possible, but loses the nuance of reproach. 'To have finished' emphasises that the deadline has passed and the action wasn't completed. Cambridge prefers the version with 'have' in contexts of unfulfilled expectation.
"You were supposed to have finished by now."
Perfect infinitive with 'supposed to': the action (finishing) should have already happened. Reproach: you were expected to have finished, but you haven't.
Why your brain gets it wrong
The learner's short circuit
Analyse the trap by exam format
People think that the artist painted this mural in the 1960s. The artist is ______ this mural in the 1960s. (THOUGHT)
Your brain constructs the impersonal passive ('is thought to') correctly, but uses the simple infinitive ('to paint') instead of the perfect ('to have painted'). It seems simpler. But 'painted' in the original sentence is past — and without 'have', the action appears present.
painted this mural in the 1960s
'Painted' (past simple) in the original sentence = past action. When transforming, 'to paint' (simple infinitive) doesn't mark past. You need 'to have painted' (perfect infinitive) to preserve the temporal reference.
→ thought to have painted
The 'have' that marks past within the infinitive
In Part 4, if the original sentence has a past tense verb (painted, stole, discovered), the transformation ALWAYS needs 'to have + PP'. Without 'have', the action loses its temporal reference. Past tense in the original → 'to have + PP' in the transformation.
Strategy
Look at the verb tense in the original sentence. Is it past (painted, left, stole)? → 'to have + PP'. Is it present (paints, leaves)? → simple infinitive 'to + verb'. The tense of the original sentence determines whether you need 'have' or not.
Experts think that the temple was destroyed by an earthquake. The temple is ______ by an earthquake. (THOUGHT)
Your brain correctly applies the pattern 'is thought to have + PP', but forgets that the original verb ('was destroyed') was already passive. 'To have destroyed' is active: the temple destroyed. But the temple WAS destroyed → you need the passive within the perfect infinitive.
was destroyed by an earthquake
'Was destroyed' in the original = past passive. You need passive + anteriority: 'to have been destroyed'. Without 'been', the temple destroys (active) instead of being destroyed (passive).
→ thought to have been destroyed
The double-layer trap: passive + perfect
When the original sentence has 'was + PP' (past passive), the transformation needs THREE layers: reporting passive (is thought) + perfect infinitive (to have) + passive infinitive (been destroyed). Many learners forget 'been' and produce an active meaning.
Strategy
Break the original sentence into layers. (1) Is it a reporting verb? → is thought. (2) Is the action past? → to have. (3) Is the action passive? → been + PP. Each layer stacks: is thought + to have + been destroyed.
The company's profits 3 significantly since the new CEO took over last year.
Option A (simple infinitive) implies they increase habitually — but 'since last year' marks a past period with a present result. Option C (*appear having) is ungrammatical: after 'appear' comes 'to + infinitive', not a gerund. Option D (*to be increase) mixes structures. Only B has the correct sequence: appear + to have + PP, indicating the increase occurred from the past until now.
'Since' + past time = perfect infinitive obligatory
When you see 'since + past moment' after 'seem/appear', you need the perfect infinitive. 'Since last year' marks that the action started in the past and reaches the present — exactly what 'to have + PP' expresses.
Strategy
Look for time markers indicating prior action: 'since', 'before', 'in the 1990s', 'last year'. If you find them after seem/appear/be said, you need 'to have + PP'. No past time marker → simple infinitive.
Perfect infinitive (to have done) is 1 of 82
The exam tests 82 grammar competencies across 19 families. Mastering one is the first step. Automating all 82 is passing.
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