GMAT Prepositions and Idioms: In and By

Prepositions in English display a powerful diversity of uses.  In previous preposition article, we talked about the proposition “on“.  Here, we will look, at the prepositions “in” and “by”.



A preposition must be followed by a noun — or by something playing the role of a noun.   This latter category includes gerunds and substantive clauses.

1) The lower tariffs, guaranteed by the worldwide treaty, resulted in opening entirely new markets to American imports.

2) The premium of a call option is not at all determined by how many open interest contracts on that option exist at any given time. 

In sentence #1, the object of the preposition “in” is a gerund phrase, and in sentence #2, the object of the preposition “by” is a substantive clause.   Incidentally, both of these are exemplary of idioms involving these prepositions.



The preposition “in” denotes containing and inclusion (“in a box“, “in my hand“, “in this book“), and this can be metaphorically extended to geographic location (“in Germany“), an area of employment (“in retail sales“), or an academic discipline (“in gender studies“).  Two important idioms involving “in” are

result in

aid in

The first is easy.  The verb “to result” idiomatically takes the preposition “in”

3) Alpha decay results in a nucleus with two fewer protons.

4) Gorbachev‘s program of Perestroika ultimately resulted in the dissolution of the Soviet Union.


Idioms involving “aid”

This is a very tricky little word.  When “aid” is used as a verb, the subject is the person providing help, the direct object is the person helped, and an “in” preposition can be used with a gerund to indicate the activity in which help was offered.

5) US Marshalls aided James Meredith in attending the University of Mississippi.

When “aid” is used as a noun, the recipients of the help can be objects of either “to” or “for” (“aid to refugees”, “aid for victims of the disaster”).   Again, the “in” preposition is followed by a gerund and denotes the activity in which help is provided.

6) His aid in stuffing the envelopes was invaluable.

7) The agency’s aid in tracking down “deadbeat dads” should not be underestimated. 

The noun “aid” can be followed by a “to” preposition to indicate a recipient, but it is a mistake to follow “aid” with an infinitive.  This is a classic idiom-mistake on the GMAT.




This verb is used in the general passive construction.  The complement of the structure P [active verb] Q is Q [passive verb] by P.

8) Fred eats the meal.  The meal is eaten by Fred.

9) Dostoyevsky wrote Crime and PunishmentThe Brother Karamazov was written by Dostoyevsky.

As a general rule, the GMAT frowns on most passive constructions for the main verb of the sentence.  BUT — notice that if we use the verb in its past participle form (i.e. “written”), we could denote a subject with a “by” preposition and use the participle to modify a noun.  This is a much more acceptable structure on the GMAT Sentence Correction.

10) Written by Dostoyevsky, The Brothers Karamazov is one of the most philosophical novels ever composed.

11) Feeling unappreciated by the Revolutionary American leadership, Benedict Arnold decided to join the British.

12) The “Caprice in A minor“, originally composed by Paganini as a virtuoso piece for solo violin, served as the basis of solo piano works by Schumann and Brahms as well as an extended concert work by Rachmaninov.

All of these use modifiers of the form [past participle]”by”[actor] — clearly, most active verbs in English could be plugged into this formula.  Two special cases deserve further attention: determined by and fascinated by.


Determined by

One verb that particularly lends itself to the [past participle]”by”[actor] modifier structure is the verb “to determine.”  If the “determining” is the main fact in a sentence, the GMAT would far prefer to see it in the active voice than in the passive voice —– “Moon phrases determine tides”, rather than “Tides are determined by Moon phases.”  It’s the nature of this verb, though, that it’s much more frequently in a modifying role I a complex GMAT-like sentence — hence, its frequent appearance in the aforementioned modifier structure.

13) Determined primarily by Moon phase, ocean tides take on bizarre and idiosyncratic patterns in enclosed harbors, such as New York Harbor and the San Francisco Bay.

14) A human is not responsible for his face during youth, a face determined almost exclusively by genetics, but arguably is responsible for his wizened face in old age, a face determined largely by lifelong emotional patterns.

15) Determined strictly by the Black-Scholes model, the price of a stock option will rise significantly when the underlying stock enters a period of volatility.


Fascinated and fascination

Finally, let’s sort out tricky idiom issue, the fascinating issue of the verb “to fascinate.”  As with all other verbs, this verb can be plugged into the modify formula: [past participle]”by”[actor].  For this verb, this is the idiom fascinated by.  This idiom, by itself, is not surprising.

16) Fascinated by the peculiarities of Dublin, Joyce filled his novels with a myriads reference to every corner of the city.

It gets trickier when we consider the noun form, “fascination.”  The noun “fascination” idiomatically takes the preposition “with” —- fascination with.  This is an important case in which the required idiomatic preposition changes when the word changes from verb to noun.

17) A lifelong fascination with the Dies Irae theme haunts all of Rachmaninov‘s major works.

Both fascinated by and fascination with are correct idioms, and very predictable mistake patterns on the GMAT Sentence Corrections are these two with the prepositions swapped —– “fascinated with” and “fascination by” — both 100% incorrect.



Know the idioms given in bold in this post.  As always with idioms, read, read, read!   Search for the idioms in this post in context.  You understand English best when you understand it in context.


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  • Mike MᶜGarry

    Mike served as a GMAT Expert at Magoosh, helping create hundreds of lesson videos and practice questions to help guide GMAT students to success. He was also featured as "member of the month" for over two years at GMAT Club. Mike holds an A.B. in Physics (graduating magna cum laude) and an M.T.S. in Religions of the World, both from Harvard. Beyond standardized testing, Mike has over 20 years of both private and public high school teaching experience specializing in math and physics. In his free time, Mike likes smashing foosballs into orbit, and despite having no obvious cranial deficiency, he insists on rooting for the NY Mets. Learn more about the GMAT through Mike's Youtube video explanations and resources like What is a Good GMAT Score? and the GMAT Diagnostic Test.