Definition:
Obligatory control is a syntactic relationship in which the implicit, phonologically null subject (PRO) of a non-finite embedded clause — an infinitival or participial clause — must be interpreted as coreferential with a specific antecedent in the main clause, either the matrix subject (subject control) or the matrix object (object control), as determined by the lexical properties of the matrix predicate. In John tried [PRO to leave], PRO must refer to John (subject control verb: try). In John persuaded Mary [PRO to leave], PRO must refer to Mary (object control verb: persuade). The syntactic-semantic constraints on which argument controls PRO are part of the lexical specification of the verb — they cannot be freely varied by the speaker.
In-Depth Explanation
PRO and Control Theory
In generative syntax, PRO (pronounced “big PRO”) is a null pronominal element that appears in the subject position of non-finite clauses. It lacks an overt phonological form but has referential properties: it must get its interpretation from an antecedent — the controller.
Control theory specifies:
- Whether the embedded clause has a PRO subject (control) or a lexical/pronominal subject (raising or full clause)
- Whether control is obligatory (the reference of PRO is fixed by the matrix verb) or optional
Subject Control Verbs
With subject control verbs, the matrix subject controls PRO:
- John₁ tried [PRO₁ to leave] — PRO = John
- John₁ managed [PRO₁ to finish] — PRO = John
- John₁ promised Mary [PRO₁ to come] — PRO = John (exceptional: promise is subject control despite having both subject and object)
Object Control Verbs
With object control verbs, the matrix object controls PRO:
- John persuaded Mary₁ [PRO₁ to leave] — PRO = Mary
- John forced Mary₁ [PRO₁ to comply] — PRO = Mary
- John told Mary₁ [PRO₁ to go] — PRO = Mary
Control vs. Raising
A key distinction: control verbs have a full argument structure in the matrix clause; raising verbs do not assign a theta role to the subject:
- John₁ seems [t₁ to be happy] — raising: seem doesn’t assign a role to John; John is the subject of be happy, raised to matrix subject position
- John₁ tried [PRO₁ to be happy] — control: try assigns an agent role to John independently
Diagnostics: a raising verb takes it as a dummy subject (It seems that he is happy); a control verb does not (\It tried that he left*).
Control in Japanese
Japanese also shows obligatory control in infinitival constructions and verb complement structures. The control pattern interacts with the rich case marking system and SOV word order. Japanese has distinctive control phenomena in complex predicate constructions using the te-form:
- Tarō-ga [ø-ga hashitte] taoreru — the null subject of the first verb is controlled by the matrix subject
Common Misconceptions
“PRO is just an invisible pronoun like English ‘you’ in imperatives.” PRO is a distinct syntactic object: it appears only in the subject position of non-finite clauses and is subject to specific control theory principles. English imperative ‘you’ is an arbitrary PRO (arbitrary control) or a specific addressee; it doesn’t fall under the obligatory control constraints that govern infinitival complements.