Q: The Hunter College Reading/Writing Center has this example of a preposition used to show manner: By doing it yourself, you save time. I’m confused. Can you explain what “by doing it yourself” is doing there?
A: “By” and other prepositions are often used with “-ing” words to form phrases that are in effect adverbial—they tell how or in what manner.
In the sentence “He supports himself by teaching,” for example, the phrase “by teaching” tells how or in what manner he supports himself.
And in the sentence “By frowning, he showed his impatience,” the phrase “by frowning” tells how or in what manner he showed his impatience.
Your sentence—“By doing it yourself, you save time”—is a similar example. How do you save time? By doing it yourself.
Those prepositional phrases (“by teaching,” “by frowning,” “by doing it yourself”) are all adverbial because they serve to modify verbs (“supports,” “showed,” “save”).
The Oxford English Dictionary says this use of “by” is especially common in the phrases “begin by” and “end by,” followed by a gerund. (A gerund is a verb form that ends in “-ing” and acts as a noun, so it’s frequently the object of a preposition.)
We found a good illustration in Dorothy Dymond’s An Introduction to Medieval History (1929):
“The barbarians began by imitating the Roman Empire, and they ended by making a group of nations. They began by accepting Christianity, and they ended by making the medieval papacy.”
When a gerund is the object of a preposition (“by teaching,” “upon waking,” “after going,” “in creating,” “without looking,” and so on), the resulting prepositional phrase has an adverbial function because it tells how or in what manner.
This might be a good place to mention that not all verb forms ending in “-ing” are gerunds. Some are participles.
The traditional wisdom is that a gerund acts like a noun. So it can be the subject or object of a verb (“fishing is his passion” … “he loves fishing”), or the object of a preposition (“after fishing he cleans his catch”).
And traditionally, an “-ing” participle is used in a progressive tense (“he is fishing”), as an adjective (“he’s a fishing fool”), after conjunctions (“while fishing, he whistles”), and in some subordinate phrases (“fishing in the lake, he caught cold”).
But today many grammarians don’t make those distinctions in terminology with “-ing” words.
As we’ve written before on our blog, Geoffrey Pullum and Rodney Huddleston, authors of The Cambridge Grammar of the English Language, prefer the term “gerund-participle.”
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