Mike MᶜGarry

GMAT Idioms of Thinking and Knowing

UPDATE: You can find this blog and others about idioms in our new GMAT Idiom eBook!

First, a couple of Sentence Correction practice questions.

1) Organizers claimed that the rally for public health care drew close to half a million people, but the city officials estimated the amount of people at the rally to be less than 300,000.

(A) the amount of people at the rally to be less

(B) the number of people at the rally to be less

(C) the number of people attending the rally at fewer

(D) that the number of people attending the rally was fewer

(E) that the amount of people at the rally was less


2) Two-time Presidential candidate William Jennings Bryan, known to oppose evolution on religious grounds, became the star witness for the prosecution in the Scopes Trials.

(A) known to oppose evolution on religious grounds

(B) known as an opponent of evolution on religious grounds

(C) known for his religiously based opposition with evolution

(D) a person who, it is known, religiously opposed evolution

(E) who, it is known, opposed evolution on religious grounds


3) Because the People’s Republic of China claims Taiwan as part of its “One China” territory and refuses to have diplomatic relations with any nation that recognizes Taiwan as an independent nation, most western nations do not have formal diplomatic relations with Taiwan, though most unofficially consider that Taiwan is an independent state.

(A) that Taiwan is an independent state

(B) Taiwan is an independent state

Improve your GMAT score with Magoosh.

(C) Taiwan as an independent state

(D) Taiwan as being an independent state

(E) Taiwan an independent state


Explanations to these questions appear at the bottom of this articles.


Idioms of Thinking and Knowing

Much of the writing on the GMAT comes from academic sources, in which people think and know all kinds of things.  The GMAT is absolutely rife with passages about folks’ thoughts and opinions and perspectives and views on assorted matters.  Relatedly, the idioms of thinking and knowing are all over the GMAT Sentence Correction.  Here are the most important ones on the GMAT:

consider A a B

consider A B

estimate A to be B

estimate that

believe that A is B

believe A to be B

hold that

think that

think of A as B

know A to be B

know A to do X

know that A is B

known as

known for

known to

The first two are covered in this post about the “consider” idioms.  Notice that the construction “consider that” is not correct on the GMAT.  The last five verbs, “estimate”, “believe”, “hold”, “think”, and “know” all can take general “that”-clauses, substantive clauses, as their direct objects, in addition to other idioms.   The topics, the subject believed or held or known, can be any fact at all.  Some of these are discussed in this post on the idioms of beliefs.


The fact that A is B

If the fact we believe or think or know is that A is B, each of these verbs has an alternate correct idiom by which to express this.  Both “believe” and “know” can take the infinitive “to be“:

5) When Henry Hudson sailed into the bay that now bears his name, he believed it to be the entrance to the famed Northwest Passage.

6) Though Sir Thomas More was judiciously silent on the issue, King Henry VIII knew him to be a devout Roman Catholic.

By contrast, the verb “think” does not take an infinitive; instead, it has its own idiom: think of A as B.  Here, “A” is a noun, and “B” can be either a noun or an adjective.

7) Opera lovers think of Renata Tebaldi as one of the most beloved sopranos of all time.

8) All modern observers think of the Dreyfus trial as blatantly unjust.



The remainder of the idioms involves the past participle “known.”  In the idiom known for P, P is the quality or ability or characteristic that made the subject famous.

9) Suzhou, known for its classical gardens and canals, has elicited comparisons to Venice.

10) The Moon is Blue (1953), known at the time for its sexually explicit dialogue and the controversy this provoked, would be regarded as a tame PG-13 movie by today’s standards. 

In the idiom known as B, B is a role occupied by the noun modified, or a quality exemplified by the noun modified.

11) Bobby Sands, known as a member of the Irish Republican Army, was elected to Parliament while he was in prison.

12) Ricin, known as highly toxic, is listed as a Schedule 1 controlled substance.

Improve your GMAT score with Magoosh.

The idiom known to, really just the passive form of the “know A to be B” idiom, is highly flexible: the infinitive following “known” can be virtually any verb in the language.

13) The father was surprised when his daughter, known to be vegan, raved about the food at the diner.

14) Known to sleep late, the teenager didn’t want an 8 am appointment.

15) Magnesium, known to burn white hot, was once the principle ingredient in a photographic flash.

16) Known to have been travelling in Southeast Asia at the time of the murder, the suspect nevertheless was charged as an accomplice.



If you had any flashes of realization while reading, you may want to give the practice questions at the top a second look before reading the solutions below.  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.


Practice question explanations

1) Split #1a: Countable vs. uncountable.  We can count people, so we speak of a “number” of people, not an “amount” of people.  (A) & (E) make this mistake.

Split #1b: Countable vs. uncountable.  We can count people, so it would be fewer people, but here we are talking about “number of people”, and for number we use “less.”   (C) & (D) incorrectly use “fewer.”  

Split 2: the correct idiom with the verb “estimate” is “estimate P to be Q“.  The option “estimate P at Q” is 100% incorrect and unacceptable on the GMAT.  (C)  makes this mistake.

The only possible answer is (B).

2) Split #1: active language.  This is not definitive, but we suspect that the verb “to oppose” will be preferred over both nouns, “opponent” and “opposition”.  Choosing the verb form of a word makes a sentence more active.

Split #2: in (C), “opposition with” is an incorrect idiom.  The correct idiom would be “opposition to”.  (C) is wrong.

Split #3: (D) contains a logic error: it changes the meaning.  The construction “religiously opposed evolution” comments on the quality of his devotion to his opposition, not the reasons for the opposition, which is the meaning of the prompt sentence.    (C) is wrong.

Split #4: Concision.  Choices (A) & (B) & (E) are all grammatically correct, but whereas (B) & (E) are wordy and awkward and indirect, (A) is sleek and elegant and powerful.  (A) is the best answer.

3) The correct idiom with the verb “consider” is consider A B.  The constructions “consider that A is B” or “consider A as B” are both incorrect.  The only answer choice with the correct idiom is (E), the best answer.



  • 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.

More from Magoosh