Infinitival Clauses and Implicit Subjects (PRO)

When a verb takes an að-infinitive complement — Ég vil fara "I want to go", Hún lofaði að koma "she promised to come" — the infinitive has no spoken subject. Yet the sentence is not subjectless in meaning: somebody goes, somebody comes, and you know exactly who. Linguists write that unspoken subject as PRO (a silent pronoun), and the central question of this page is how PRO gets interpreted — who the silent goer is. The answer is one of three: it is controlled by the matrix subject, controlled by the matrix object, or read arbitrarily ("anyone, people in general"). The deepest and most Icelandic point comes at the end: PRO can carry quirky case, visible through a predicate that agrees with it — proof that Icelandic assigns case even to a subject you cannot hear. (This page is the companion to raising, ECM, and control, which contrasts control with raising and ECM; raising and modal bare infinitives are treated there and in the Verbs group. Here we go deep on PRO and its control.)

What PRO is: a silent, interpreted subject

PRO is the understood subject of an infinitive. It is silent — you never pronounce it — but it is grammatically real: it heads the infinitive's clause, it is the thing the infinitive predicates over, and (as we will see) it can even bear case. The að before the infinitive is the infinitive marker; the controller that fixes PRO's reference sits up in the matrix clause. The skeleton is matrix verb … [að + infinitive], where the bracketed clause has the silent PRO as its subject:

English has the very same silent subject ("I want to go" — to go has no spoken subject either), so the concept transfers cleanly. What does not transfer is the morphological evidence Icelandic gives for PRO's existence — and the requirement that you not fill PRO with an overt pronoun when it is coreferent.

Subject control: PRO = the matrix subject

In subject control, the controller is the matrix subject — the silent goer is whoever the higher verb's subject is. This is the default for verbs of wanting, intending, deciding, promising, hoping, trying: vilja "want", ætla "intend", ákveða "decide", lofa "promise", vona/vonast "hope", reyna "try". With these, the matrix subject is the lower subject — they corefer obligatorily.

The defining property: with a subject-control verb, you cannot add a separate lower subject, because there is already one — the silent PRO, locked to the matrix subject. \Ég reyni hann að koma is impossible; if the comer is someone else, you must switch to a *finite clause (Ég vona að hann komi "I hope that he comes"), not a control infinitive.

Object control: PRO = the matrix object

In object control, the controller is the matrix object — the silent doer is the person the higher verb acts on. This is the pattern for verbs of asking, ordering, forcing, allowing, persuading: biðja "ask", skipa "order", neyða "force", leyfa "allow", fá (e-n til) "get (someone to)". The matrix object names the doer of the infinitive.

The contrast with subject control is the whole game: Ég lofaði að fara (subject control) = I go; Ég bað hann að fara (object control) = he goes. The matrix verb's meaning decides which argument controls — promising commits the promiser, asking commits the askee. English works identically ("I promised to go" = I go; "I asked him to go" = he goes), so the logic transfers; you are only learning which Icelandic verbs fall into which class.

Arbitrary (generic) PRO: "anyone, people in general"

Sometimes there is no controller at all — the infinitive has no matrix subject or object to corefer with, and PRO is read arbitrarily: "anyone, one, people in general". This is arbitrary (or generic) PRO, typical of impersonal evaluative frames — Það er gott/erfitt/hollt að … "It is good/hard/healthy to …" — where the silent subject is a generic "one".

Note the reflexive sig in hreyfa sig — it must be reflexive (not hann/hana) precisely because it is bound by the silent generic subject; this is one of the diagnostics that an unspoken subject is really there. Arbitrary PRO corresponds to English generic "one" or the impersonal "to + verb" in "it is good to exercise".

The startling fact: PRO can carry quirky case

Here is where Icelandic, again, lets you see what other languages keep hidden — and the single most sophisticated point on the page. PRO is silent, so you might think it has no case. But Icelandic assigns case to subjects even when they are silent, and you can detect it through a word that agrees with PRO and shows its own ending — a floating quantifier (allir "all", einn "alone") or a secondary predicate inside the infinitive. When the lower verb is a quirky-case verb — one that assigns a dative or accusative to its subject — PRO gets that quirky case, and the floating quantifier surfaces in the quirky case, not the default nominative.

Take leiðast "be bored", which assigns dative to its subject (mér leiðist "I'm bored"). Put it under a control verb and add a quantifier that ranges over the silent PRO: that quantifier shows up dative, because it agrees with a dative PRO you never pronounce. Contrast it with an ordinary nominative-subject verb, where the same quantifier is nominative:

The diagnostic is the minimal pair: one verb (leiðast) hands PRO a dative, the other (komast) a nominative, and the quantifier — öllum vs allir — faithfully records which, even though the subject it agrees with is unspoken. The logic is exactly parallel to case preservation under raising (see the raising page): just as a raised quirky subject keeps its dative, a controlled silent subject receives its quirky dative. The conclusion linguists draw is striking: case is assigned to subjects independently of whether they are spoken — silent PRO has case just as overt subjects do, and Icelandic is the language where the ending on an agreeing quantifier peeks through to prove it.

Why English speakers stumble: the overt-pronoun trap

The biggest production error has nothing to do with case and everything to do with English's that-clauses. When the lower subject is coreferent with the matrix subject, English freely allows a finite clause with a repeated pronoun — "I want that I go" is bad in English, but "She said she would go" is fine, and learners over-generalise, producing \ég vil að ég fari "I want that I go" instead of the control infinitive ég vil fara. *When the embedded subject is the same as the matrix subject, Icelandic requires the control infinitive (PRO), not an overt repeated pronoun in a finite clause. The overt pronoun is reserved for a different subject (ég vil að hún fari "I want her to go" — finite, because the goer is someone else).

The second error is mis-assigning control — reading subject control where the verb is object control, or vice versa. Because the controller is fixed by the matrix verb's meaning, you must know whether the verb commits its subject (lofa — I do it) or its object (biðja — you do it). Get the verb class wrong and you misidentify who acts.

Common Mistakes

Coreferent subjects force the PRO infinitive; the repeated ég in a finite clause is an English-style calque.

After object-control biðja, the infinitive is introduced by að; the matrix object hann controls the silent PRO.

Subject-control verbs lock PRO to the matrix subject; you cannot insert a different doer into the infinitive.

The control infinitive means the promiser acts; to attribute the action to someone else, switch to a finite (subjunctive) clause.

Arbitrary PRO still binds a reflexive: hreyfa sig "move oneself", not hreyfa hann.

Key Takeaways

• An að-infinitive has a silent subject, PRO; its reference is fixed by a controller in the matrix clause. Reading control = identifying which matrix argument PRO corefers with.
• Subject control (vilja, lofa, reyna, ætla, vona): PRO = the matrix subject — the promiser/tryer does it. Object control (biðja, neyða, leyfa, skipa): PRO = the matrix object — the askee/forced one does it. Same logic as English "promise to" vs "ask … to".
• Arbitrary (generic) PRO has no controller — "anyone, one" — typical of impersonal frames (Það er erfitt að læra íslensku); it still binds reflexives (hreyfa sig).
• The startling fact: PRO can carry quirky case. Under a quirky-case verb (leiðast, líka), the silent PRO is assigned dative/accusative, visible through an agreeing floating quantifier (öllum dat. vs allir nom.) — proof that Icelandic assigns case to subjects even when they are unspoken, mirroring case preservation under raising.
• The English transfer trap: when the lower subject is coreferent with the matrix subject, use the PRO infinitive, not an overt repeated pronoun (ég vil fara, not \ég vil að ég fari). An overt finite clause is for a *different subject (ég vil að hún fari).