Q: I’m interested in hearing what you think about the use of the infinitive in “I’m interested to hear what you think.”
A: Let’s begin by discussing the use of “interested” with “to hear” and “in hearing.” We’ll get to other complements later.
English speakers have used both constructions (“interested to hear” and “interested in hearing”) for more than two centuries, but the one with the gerund (“hearing”) is more popular today than the one with the infinitive (“hear”)
The two usages are now common in both the US and the UK, according to our searches of the Corpus of Contemporary American English and the British National Corpus.
The verb “interest” is being used here in the passive voice (“to be interested”) with the sense of “I desire hearing what you think” or “I want to hear what you think.”
The earliest example we’ve found for “interested to hear” is from an Oct. 26, 1819, debate among the delegates at a Maine constitutional convention: “You are deeply interested to hear more!”
The first example we’ve found for “interested in hearing” is from Early Lessons, an 1825 collection of children’s stories by the Anglo-Irish writer Maria Edgeworth:
“Now she could hear Frank’s thoughts and feelings about every thing and every person they had seen at Bellombre; but chiefly she was interested in hearing that his father and mother were quite satisfied with him.”
The Oxford English Dictionary has several gerund and infinitive examples with verbs other than “hear,” including one from the late 1700s in which “to be interested” is used with an infinitive. We’ll have more about this when we get to the etymology of the verb “interest.”
Although the gerund usage is more popular now, the infinitive usage has been more popular at various times in the past, according to a search with Ngram Viewer, which provides rudimentary comparisons of phrases in the millions of books digitized by Google.
As for your question, we find both “interested to hear” and “interested in hearing” acceptable, but the gerund usage is more idiomatic, or natural, to our ears, and we rarely use the infinitive construction.
Things get more complicated when “to be interested” is used with the gerunds and infinitives of verbs other than “hear.”
In “The Lexicogrammar of Be Interested,” the linguist Costas Gabrielatos points out that the gerund construction is used with many more verbs than the infinitive.
Gabrielatos, whose paper analyzes the use of “be interested” in various English corpora, or databases of recorded language, writes that the infinitive usage “seems to have a much more restricted range of complements” than the gerund usage.
He says he found that the infinitive is usually used with verbs of perception or inquiry, such as “find,” “hear,” “know,” “learn,” “note,” “read,” “see,” and “share.”
Our own examination of American and British corpora, which reflect the language as it’s actually used, indicate that “interested to” is generally used with verbs of perception while “interested in” is used with verbs of both action and perception.
So one might be “interested in seeing” or “interested in going” to a movie, according to these databases. However, it’s more likely that one would be “interested to see” a movie than “interested to go” to it.
As we’ve said, the gerund usage sounds more natural to us—and that’s the case with verbs of perception and verbs of action.
We should note, however, that we’ve used the infinitive construction a few times on our blog, and that we haven’t found any objection to it in the many grammar and usage manuals in our library.
As for the etymology here, the verb “interest” showed up in the early 17th century as a variant of the now-obsolete verb “interess.” The ultimate source is the classical Latin interesse (to differ, concern, be of importance).
The OED notes a suggestion that the “interest” spelling “might be partly due to confusion” with “interessed,” the past tense of “interess.”
The dictionary defines the verb “interest” in the sense we’re discussing as to “cause (a person) to have an objective interest or concern in the progress or fate of a matter; to involve.” It says the usage is chiefly seen in the passive construction “to be interested.”
The first Oxford citation is from Essaies Politicke and Morall (1608), by the Anglican clergyman and auhor Daniel Tuvill: “When they think he is not interested in the cause, or induced by any priuate obligation.”
And here’s a negative 1781 example for “to be interested” with an infinitive, from The History of the Decline and Fall of the Roman Empire, by Edward Gibbon: “The emperor himself was interested not to deface the splendour of his own cities.”
Finally, here’s an OED citation for “to be interested” used with a gerund, from an 1886 decision of the Chancery Division of the High Court in England: “The landlord … is interested in seeing that the liquidators discharge their duty properly.”