We discussed this sentence in a writing group this week:
*The purpose of IDEA is providing …
(IDEA = Individuals with Disabilities Education Act)
The non-finite -ing form providing is incorrect here: the sentence should read:
The purpose of IDEA is to provide …
This type of sentence occurs with a linking verb such as be (also known as a copular or relational verb). The to infinitive clause (to provide) functions as the complement of the subject (the purpose of IDEA). That is, the clause after the main verb (is) “further identifies or describes the subject of the main clause” (LGSWE, p. 714-5).
This structure is most common when the subject of the sentence is:
- abstract (hope, purpose, concern, answer, function, response)
- a step in a process or argument (the first step is to, the second problem is to)
- an aim, objective, plan, goal, purpose, strategy, task, or idea
- a method or way of doing something
- a to infinitive clause itself
This pattern is fairly common in written English, although less so in spoken English. (Source: Longman Grammar of Spoken and Written English)
There are situations where an ing verb is possible: the Longman grammar gives this example:
The movement’s greatest hour was fighting against an attack on the movement.
But I couldn’t find more about this. I suspect the -ing clause is less common in this position. Generally, to clauses are more abstract than ing clauses, which tend to refer to actual actions. This might help explain this pattern.
Some examples of to infinitives after linking verbs from the MICUSP corpus of student writing:
- the aim of this paper is to assess these arguments and suggest some possible common causes
- the goal now is to follow changes in the intracellular electric field
- the challenge for epidemiologist nowadays is to have an
epidemic-anticipatory-capability
for the appearance of new strains - The goal of the program is to halve malarial deaths in target sub-Saharan African nations
- One way to prevent cardiovascular disease is to reduce risk factors
- if Aristotle’s purpose is to distinguish belief from phantasia …
