I corrected a student as she had made the sentence "it's ok to Martin". I know that this sentence structure is incorrect, she asked why I had made the correction and I am having difficulty explaining why. Anyone care to help?
The sentence seems ok to me. It appears to me like your student was right, assuming she was using it in the right context. Why wouldn't it look ok to you? Do all of these sentences sound natural to you?
The expression "to (pro)noun" is used all the time with a number of verbs, such as in the sentences above. Here is some evidence, in the form of random internet quotes, that "to be" is commonly used like this:
Because a) it's clearly not OK to him, and b) I just met him, so I don't really give a damn.
Bad With Men: For the Love of Benji
He felt he could flirt and say whatever yet it was ok to him because he wasn't acting out on it.
Ask a Guy: My Boyfriend Flirts With Other Women
What matters is if your lifestyle is ok to you.
Is it OK to never marry?
If the flag is burnt because of the country it represents (in this case, America) then it definitely wouldn't be OK to Americans.
If an American flag was made in China, is it ok to burn it?
In fact, even Brooks' controversial stand against selling used compact discs in stores was OK to his legions outside.
Garth Brooks Hasn't Thrown in the Hat on Used CD Controversy
Another example is on Twitter (NSFW language).
The history is all in the Oxford English Dictionary under this definition of "to":
Used esp[ecially] after be, become, seem, appear, mean, to indicate the recipient of an impression, the holder of a view or opinion; to be (something) to, to be (something) in the eyes, view, apprehension, or opinion of; also, to be of importance or concern to: what is that to you? What does that matter to you? How does that concern you? What have you to do with that?
It's pretty old, with a version of "what's that to you" appearing in the West Saxon Gospels around AD 1000 ("Hwæt to þe?", literally: what to thee?). The Middle English Dictionary says that it was "usu[ally] rendering, or imitative of, a L[atin] dative of possession", which makes sense seeing how the verb is missing in some of the Middle English examples, since one Latin guide says "The Dative of Reference is used idiomatically without any verb in colloquial questions and exclamations." The "in x's opinion" sense came a little later, with "As hit semeþ to vre siht" (literally as it seemeth to our sight) appearing in Piers Plowman (1362).
The student is right from a technical perspective because it has a subject and predicate, but it is not good for learning proper form.
This is a conversational response, and should be allowed even in classroom conversation, but it should not be used in formal study of "proper" English in writing.
Expansion of the likely meaning:
It [which was mentioned previously] is okay in Martin's opinion.
That would be the literal interpretation of this sentence. If that was not the student's meaning, then it was "wrong" on account of expressing the wrong idea.
From a "proper form" perspective, there are two big problems, a greater and a lesser...
The main problem is that the pronoun "it" has not been specified.
A lesser problem, but one of the tasks of English instruction, is to address over-use of the "being" verb; the sentence would be helpfully clearer to employ creative use of a verb other than "is".
[NOUN OR PHRASE] seems okay to Martin.
From one teacher to another, I will add a pedagogical note that it is vital to explain these two points in very simple terms to a younger student, perhaps: Don't use "it", use the noun you mean. And, "is" seems too boring, be creative. But, I don't want to over-think for you, just being clear. ;-)
As a second note on defining "proper" English, unlike Chinese where the government defines words and form, English is only "correct" according to accepted styles, e.g. British vs American, neither of which is government approved. Our "standards" come from institutions like Oxford, University of Chicago, MLA, AP, et cetera. Many "correct" English papers are rejected from journals for not using "academic" form, likewise a newspaper editor would reject an article fit for a journal for not using "newswriting" style. So, this is a great opportunity to prepare your students for real life by explaining the "style used in our classroom" rule as it applies in this situation.