For the record, "“acting strangely” is grammatical.
Unless you are an illiterate American, an adverb must be used to describe a verb. Would you prefer “acting strange”?
Over the past few decades, US English has taken the strange (yes, not “strangely”) decision to rid itself of many of its adverbs, hence “You did good” and “It was all over real quick”.
It’s ugly, it’s wrong and it’s spreading. Part of the blame should be shovelled onto Cecil’s head.
I’m sure sterner linguists will clarify, but you’ve missed the point.
Christopher Walken acts strangely. A schizophrenic acts strange.
“You did good,” while potentially misused, is perfectly grammatical, something you might say to Mother Teresa.
Wha…?
Cecil “won’t argue” with the main contention of the querist in the article, and he calls “act” a linking verb. “Not arguing with” is not the same as “endorsing”. (This is my weaselly way of avoiding contradiction of the Perfect Master.)
“Act” is a verb. In the present context, it can be replaced with “behave” without change of meaning. And how does the schizophrenic behave? Noting that adverbs modify verbs by describing such things as how, when, where and why, the answer must be “strangely”. Any other conclusion must surely be an American variant.
To swap “act” for “appear” or “seem” is an imperfect substitution. “Appear” and “seem” emphasise the relatively passive position of a beholder, not the active behaviour of the schizophrenic.
Having said all of that, ultimately I suspect this is not capable of being resolved by reference to iron rules. As observed above, the ear is led by local idiom, and it is quite possible for one variant to appear strange to an American speaker of English and the other to appear equally strange to a Commonwealthian. Just one of those “divided by a common language” things.
There seems to be a lot of that about, doesn’t there? 
“You did good” is perfectly good as the past tense of “You do good”, inasmuch as “good” is a noun as well as an adjective. “It was all over real quick”, on the other hand, is no more acceptable in the US than anywhere else.
For the record, both “He was acting strangely” and “He was acting strange” are grammatical, since many verbs can be used with both adverbs and adjectives. There – I feel good at having got that off my chest … and no, I don’t feel well as a result of it (either with “well” as an adjective, or with “well” as a adverb.
You use adjectives after verbs if they describe the condition or apparent condition of the subject, so you can be strange, look strange, appear strange, or act strange. An adverb describes the action of the verb, so you would say a person was acting strangely if their actions were strange.
And since there’s a considerable overlap between a person acting in a way to makes them appear strange (“acting strange”) and a person acting in a strange manner (“acting strangely”), often you might use either phrase to describe the same situation.
It wouldn’t be acceptable in the written form perhaps, but “it was all over real quick” would be perfectly acceptable colloquial speech around here.
First off: Bleh.
In particular: “Unless you are an illiterate American, an adverb must be used to describe a verb.” This is a misleading analysis; after all, copulas are generally verbs, and certainly, one who says “act strange” is using “act” as a copulative verb. Consider “John is tall” or “John seems tall” or “John looks tall” or any example from here; following a verb with an adjective in this way is hardly unusual at all.
If you’ve got the flu you feel bad; if you’re wearing oven gloves you feel badly.
As for “acting strangely”, it sounds a lot better to my ear than “acting strange”.
Certainly, there may be regional differences in whether or not “act” can function as a copulative verb in your dialect. Though I disagree with most of Noel Prosequi’s post, I agree with
[Note that he follows (“describes”, “modifies”) the copulative verb “appear” here with the adjective “strange” rather than the adverb “strangely”, which has gone entirely without comment but serves well to illustrate that there is nothing particularly anomalous about this kind of syntactic structure]
I think it’s because “appears” is a passive verb, but “acts” is active. So you appear (to be) strange, but you act in a strange manner, i.e. strangely.
What do you mean by “passive verb” and “active verb”? In standard grammatical terminology, both “John appears strange” and “John acts strange” are in the active voice, not the passive voice, and I am actually hard-pressed to think of any natural examples using “appear” in the passive voice, given that its use, apart from as a copula, is intransitive (for “act”, I suppose a passive voice example is “The play is acted by high school students”, though it is a little awkward, and, of course, does not use “act” copulatively).
I suppose you may be using “passive verb” to denote copulas and “active verbs” to denote other uses of verbs, in which case you’d be saying the right things but with unusual, possibly misleading terminology [but then, the standard terminology is pretty misleading too…].
The letter writer in Cecil’s column has exemplified the rule that one who points out spelling or grammatical or usage errors in another’s writing will himself make spelling or grammatical or usage errors in the process; I believe there’s a Law of the Straight Dope Message Board to that effect.
But, to clarify my post: to me, a US Southerner, “acting strangely,” referring to a person whose behavior is strange, sounds pseudo-erudite, as if the writer learned in college that all verbs must be followed by an -ly adverb, and wants to display his superior English skillz to the masses. I understand that either formulation is grammatically correct, and that my take may be regional.
And I will always cringe when my mother-in-law says “I feel badly for X.”
I think this went without comment because Noel Prosequi intended it to be illustrative of his own point, i.e. that “appears” is a proper linking verb while “acts” is not.
I admit I made up the terms, for want of a better explanation, but do you not see what I mean? The verb “appears”, in the sentence “John appears strange”, describes how someone else perceives John. It’s not anything that John is actively doing himself. So, you could equally say “John appears (to other people) to be strange.”
With “John acts strangely”, though, “acts” describes something that John is actively doing. He is acting in a strange way, i.e. strangely.
I looked up the definition of “copula” and I can’t say I fully understand the concept, which is why I used “passive” and “active” to differentiate between the verbs.
Here’s the best example I can come up with: “John looks strange (to me)”, but “John looks strangely (at his brother)”. What is the technical name for the difference between these uses of the verb? Both are in the active voice, but the meanings are very different.
Yes, the technical name for the difference is that “looks” in “John looks strange” is a copula while “looks” in “John looks strangely” is not (some non-linguists use the term “linking verbs” for copulative verbs and “action verbs” for non-copulative verbs, which would be closer to the terminology you were using).
However, it’s important to note, the distinction between the two lexical categories is not essentially semantic but, rather, syntactic; that is, it isn’t fundamentally about the meaning of the sentences being expressed and some judgement about whether this is a statement more primarily about perception or about activity, although there may be some frequent correlation. Rather, the distinction has to do with what the “shape” of the sentence is, which particular grammatical construction it exemplifies and what role the words within it play in that syntax tree.
For example, “John appears hungry” and “John exudes hunger” both mean the same thing, an observation about a perception regarding John; however, in the first, we have a copula followed by an adjective, while in the second, we have a (non-copulative) transitive verb followed by a noun. Similarly, “The gel became hard” and “The gel hardened” both mean the same thing, an observation about an action undertaken by the gel; however, in the first, we have a copula followed by an adjective, while in the second, we have a (non-copulative) intransitive verb.
To make the point another way, even having no idea what the sentences mean, you can still tell that “John proxnabbed jorbicious” is copular while “John gabsmogged jorbiciously” is not.
(At least, insofar as you can tell that “proxnabbed” and “gabsmogged” are verbs in the preterite, while “jorbicious” is an adjective and “jorbiciously” an adverb). The point being, judgements about the meaning of the sentence aren’t necessary for determining the syntactic properties (and thus, well-formedness/grammaticality at the syntactic level [in the same sense in which “Colorless green ideas sleep furiously” is easily seen to be well-formed/grammatical without any prerequisite invention and analysis of some spurious pseudo-meaning]).
Way to act like a jerk while missing the point altogether. As pointed out above, the word “strange” need not be seen as describing “act” in this sentence.
It’s like saying “She looks pretty.” I wouldn’t say “She looks prettily,” unless I mean “She looks at things in a pretty way.” If, as is more likely, I mean that she has a pretty appearance, then “She looks pretty” is correct.
Likewise, one who “acts strangely” has a strange way of acting, whereas one who “acts strange” behaves in the manner of one who is strange. Since there’s not much distinction between acting strange and being strange, the difference is more subtle than in the case of “looks pretty” vs. “looks prettily”.
Cecil’s response was perfect.
In the original context – a direct quote – the grammar is as right as it needs to be. Whether the grammar is right or wrong, the journalist (who is ultimately the letter writer’s target) is trained to put it in writing exactly it as was spoken. In the context of being a written transcript of actual words spoken by a real person, ‘acting strangely’ is the only right answer.
“Feelings of inferiority arise from inferior feeling, and that’s not just a play on words.”
– Carl Jung
(quoted from memory, your memory may vary)