Grammatically, you should use the adverbs. But you will see and hear "weird" after those verbs.
Student or Learner
I'm a little confused. Should we use adjectives or adverbs after behave/act?
Which one is more idiomatic?
To act so weird
To act weirdly
To behave impolite
To behave impolitely
I would be glad if you could give me your opinion. Thank you.
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***** NOT A TEACHER *****
You have already received the answer.
I am replying only because I have found some information that may interest you.
The verb "act" has always driven me crazy, too, so I have collected the opinions of various people. I am delighted to share a few.
1. "The [indigenous people] acted friendly.
a. My source tells me that we can think of "friendly" as an adjective in such a sentence.
i. It means that they seemed/were friendly. [As you know, "seem" and "were" are linking verbs.]
b. The source says that the same applies to "He acted silly."
i. But we cannot say, "He behaved silly/stupid."
Authority: Robert M. Gorrell, Watch Your Language.
2. One netizen who seems very knowledgeable says this:
a. "Act" is frequently treated as a linking verb.
i. It is similar to "seem."
(a) "He acts (as if he were) smart."
Source: A netizen named "CalifJim" at a grammar helpline called englishforums.
3. "Act" is often a linking verb -- according to another authority.
a. In this sense, it means to pretend to be something.
i. "Stop acting innocent."
ii. "If anybody asks, act dumb."
Authority: Merriam-Webster's Learner's Dictionary.
4. Finally, one scholar gets very upset when people say, "Act natural."
a. He says that such a sentence is a "pure Germanism." He adds: "Though in common use by Americans, [it is] recognized as slang."
I have made up this dialogue that I think would please that scholar.
Mona: I hear that you have a job interview today.
Raul: Yes, and I'm very, very nervous.
Mona: Don't be nervous. Just act naturally, and they will hire you.
Authority: Michael Dummett, Grammar & Style for examination candidates and others (1993).
Last edited by TheParser; 25-Oct-2015 at 09:58.