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A Tricky GMAT Idiom: “act like” vs. “act as”

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

First of all, try this Sentence Correction question.  A full explanation will follow later in the post.

1) Whereas both Europe and China use standard railroad gauge (1435 mm), Russia deliberately chose the wider “Russian gauge” (1520 mm) that gives greater side-to-side stability in railways cars and, more importantly, acts as a national defense, so that it would block foreign army’s supply line and preventing these bordering powers from invading by train.

  1. acts as a national defense, so that it would block
  2. acts like a national defense, so as to block
  3. acts as a national defense, blocking
  4. acting as a national defense, blocking
  5. acting like a national defense, would block


“Like” vs. “As”

As I explain in the post linked above, in general “like” is followed only by a single noun, and is used to compare nouns; but “as” is followed by a full noun + verb clause, and is used to compare actions.

2) This rookie swings like Ted Williams.

3) Ted Williams leads the majors in career on-base percentage, as Babe Ruth leads in career slugging percentage.  Each is in second place behind the other on the respective lists.


The Idiom: “act like”

You will get a lot of mileage out of the general rule for “like” vs. “as”, but it is no longer a reliable guide when you get to this idiom.

In English, the idiom “to act like” means to behavior or comport one’s self in imitation of something else.  If I “act like a king”, that implies that I am not a king, but something about my behavior (presumably, my entitlement and presumption) resembles that of a king.  A person is capable of intending to imitate something, so a person can “act like” something.  Conceivably, an intelligent animal (one of the higher primates, for example) could be induced to imitate something, in which case we could say: the chimpanzee “acts like” such-and-such.  Any inanimate object is utterly devoid of intentionality, so we cannot in any way attribute imitative behavior to it: therefore, we can never use the idiom “act like” with an inanimate object.  With an object, we always have to use “act as.”


Explanation of the Question

First of all, from the foregoing discussion, we know that the inanimate object “Russian gauge” cannot “act like” anything, because it doesn’t have the conscious ability to imitate.   If the subject is an inanimate object, we need to use “act as”.  Thus, (B) and (E) are out immediately.

We also have two parallel constructions we need to maintain here.  We need the two verbs following “Russian gauge” to be in parallel —- the first is “gives”, so the second has to be the parallel “acts” —- thus, (D) is out.

The second parallelism is between “would block”/”blocking” and the participle “preventing”; clearly, we need the participle “blocking” for the first verb.  Therefore, (A) is out, and the only correct answer remaining is (C).


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14 Responses to A Tricky GMAT Idiom: “act like” vs. “act as”

  1. Anche June 24, 2014 at 4:21 am #

    Hi Mike,
    Could you explain the below one
    “sensor acts as a radar” or “sensors acts like a radar”

    As per the article inanimate object uses “act as”. in the above example sensor is also an inanimate object.

    when i googled i found many results with “sensors acts like”

    Could you also explain in case of animated objects like car/bus/train. how to use act as/act like.

    please help me to understand.


    • Mike
      Mike June 24, 2014 at 11:43 am #

      Dear Anche,
      First of all, understand that not every who is fluent in English uses good grammar. In fact, I would say that many many Americans, native English speakers from birth, make all kinds of grammatical mistakes. Websites in English, even when written entirely by native speakers, can be loaded with grammatical mistakes. The GMAT holds very high standards for grammatical precision, and many individual Americans or individual websites will fall quite short of these standards. If a phrase appears frequently in a web search, that is absolutely no guarantee that it is correct or even minimally acceptable. I am quite sure you could find any grammar mistake all over the web.

      The rules given in this blog describe the standard held by the GMAT and by all sophisticated sources — academic books and journals, high quality newspapers such as the New York Times, high quality periodicals like Harpers, or Atlantic Monthly, or the Economist. Most websites do not come anywhere even vaguely close to these high standards.

      If you want to know what is grammatically correct, do not use Google. Stick to high quality GMAT sources and high quality writing in English.

      For the GMAT, “act like” is never used with an inanimate object (sensor, bus, car, train, etc.) To say X “acts like” something is to attribute will and intention to X — we may say that of an animal, but it is illogical to predicate that about an inanimate object.

      Does all this make sense?
      Mike :-)

      • Anche June 24, 2014 at 8:54 pm #

        Yes it make sense.
        Thanks a lot Mike.


        • Mike
          Mike June 25, 2014 at 1:23 pm #

          Dear Anche,
          You are quite welcome. Best of luck to you!
          Mike :-)

  2. Nishant October 8, 2012 at 9:38 pm #

    Mike: I selected option D for parallelism acting/blocking….
    Why can’t these two be parallel. Why act has to be parallel with gives?

    Can’t we say……

    The railroad gauge gives greater stability……..acting as anational defence, and blocking…….

    I guess “and” is necessary…is it?

    • Mike
      Mike October 9, 2012 at 2:00 pm #

      Dear Nishant:
      The verb “act” is NOT parallel to the verb “block” — the verb “act” is parallel to the verb “gives” (in the pre-underline section), and so much be parallel to that. Think about the subject of the verb “act’ — if you follow back to the subject of that verb, you see it has to be parallel to “gives”
      “… Russia choose the wide gauge that gives ….. and …. acts” — that’s why “acts” is correct and “acting” is 100% wrong. The “block” verb need to be parallel the participle “preventing”, so it must be in the form “blocking.”
      Does all this make sense?
      Mike :-)

      • Nishant October 9, 2012 at 7:53 pm #

        Mike: Thanks, yes it all does make sense. If it were given “and prevents” instead of “preventing” then It would have been “blocks”. Am I right?


        • Mike
          Mike October 10, 2012 at 10:04 am #

          Mike :-)

      • KC April 3, 2014 at 9:50 am #

        What does the participle ‘blocking’ modify in this sentence? Is it the Russian guage? I ask because I read somewhere that the noun a participle modifies should be the sentence of that sentence if the participle were to take the -ing form, as happens in this case!
        2. Would the participle take the -ed form had the noun been the object of the noun modifier in questions? Can you please shed further light on this topic, please
        Lastly, your blog is the best there is! Odd choice perhaps, but riveting is the word! :)

        • Mike
          Mike April 3, 2014 at 10:18 am #

          Dear KC,
          The parallel modifies “blocking … and preventing” simply modify the word they touch, “national defense.” The national defense blocks and it also prevents.
          Did you mean to say: “…the noun a participle modifies should be the SUBJECT of that sentence if the participle were to take the -ing form…”? If the present participle (the -ing participle) modifies a NOUN, then yes, that noun should be the subject of the action of the participle, but if the present participle modifies an entire clause, as it sometimes can do, then the implied subject may not be stated explicitly.
          Yes, the present participle (the -ing form) is an active participle, and the past participle (often the -ed form) is a passive participle. The present participle modifies a subject, and the past participle modifies an object. See:

          Finally, thank you for your kind words. I am sincerely pleased that you find it helpful.
          Mike :-)

  3. Yesh July 20, 2012 at 11:04 am #

    Hey Mike,

    I think Magoosh should offer some practice tests for GMAT. I honestly feel you and Chris do a perfect job with GMAT questions. I didn’t come across better tutors than you guys. Only thing, if you guys can come up with some practice tests that would be great. There are lot of guys like me who are waiting to buy practice tests from magoosh.


    • Mike
      Mike July 20, 2012 at 11:55 am #

      Yesh: Thank you for your kind words. It’s true we don’t have a single-button for a practice test, but it’s really not very hard inside the Magoosh product to set up a CAT section for yourself. On the “Practice” page, you would select math or verbal, then difficulty = “Adaptive”, Pool = (your preference), Number of Questions = 37 for Quant or 41 for Verbal, and Time Limit = 75 minutes. Voila! You have a CAT section. Write a practice essay, do the IR questions, then do a Verbal section and a Quant Section — that’s a full practice GMAT, with CAT on the Q & V sections. Again, we don’t package it already designed — you have to set it up yourself, but that takes less than 30 seconds, and then you are good to go. Does that make sense?
      Mike :-)

  4. Faruk July 19, 2012 at 9:55 am #

    Mike,is the use of ‘it’ in the answer choice A wrong ?

    • Mike
      Mike July 20, 2012 at 10:44 am #

      Faruk: actually, in choice (A), the singular pronoun “it” correctly refers back to the singular antecedent “Russian gauge.” Perfectly correct. Parallelism is a problem in (A), but not the pronoun.
      Mike :-)

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