Can a noun in a sentence be both in the nominative and accusative cases?

Question

One of my teachers once said that a noun in a sentence is always in a certain grammatical case and always has a certain role - the subject or an object. In other words, no noun can be in two different grammatical cases at the same time and play a dual role.

Being a curious thinker, I decided to challenge the validity of that statement.

Since many nouns have the same form in the nominative and accusative cases, I decided to use it to construct a sentence in which a certain noun is the subject for one verb and the object for another verb and is thus both in the nominative and accusative cases. I came up with this:

Его мнение о тебе неважно и к тому же можно исправить. (His opinion about you is unimportant and also can be changed.)

My idea is this: the noun "мнение" here is the subject (подлежащее) for the first part of the sentence and the object (дополнение) for the second part of the sentence. That is, the noun "мнение" is in the nominative case in relation to the missing verb (zero copula) of the first part of the sentence and in the accusative case in relation to the verb "исправить." Voila.

My question is this: Are my sentence and analysis correct? I am very curious as to whether I can make such sentences and whether I proved my teacher wrong.

---

UPDATE: My question appears to be more tricky than I thought. On the one hand, initial responses below indicate that my sentence does not sound natural and is грамматически несогласованное предложение. On the other hand, I found various examples of similar sentences on the Internet:

Остальное неважно и можно выяснить потом. (Source)

Остальное неважно и можно забыть. (Source)

Пока ты любишь меня, все остальное неважно и можно пережить. (Source)

Answer 1

The sentence does not sound as native Russian to me.

First, you should use a pronoun in the second part to refer to «мнение»:

Его мнение о тебе неважно и к тому же его можно исправить.

Or you may use «это» to refer to the situation as a whole:

Его мнение о тебе неважно и к тому же это можно исправить.

This answers your main question, but there are more flaws in the sentence.

Second, we need a comma between the parts.

Third, the word «неважно» here is ambiguous. It has two meanings: “unimportant” and “bad/negative”. See its Wiktionary entry. If you meant the first, you should write it with space to avoid ambiguity:

Его мнение о тебе не важно, и к тому же его можно исправить.

or even add some words in between to avoid ambiguity in speech too:

Его мнение о тебе не так важно, и к тому же его можно исправить.

There seems to be no strict rule whether to write it with space or not (see this question), but if it helps avoid ambiguity, I think you should use space.

More articles on «неважно»/«не важно» problem: russkiiyazyk.ru, gramatik.ru, mel.fm.

If you want to say that the opinion is bad, then you should better write it with full adjective «неважное». In that case, the choice of connecting words sounds weird. «И», and even stronger «и к тому же», are for connecting non-contrasting statements, and your statements do contrast. You should either use «но» (another contrasting conjunction is «а», but I don’t see how to put it here), or make statements non-contrasting. So, two variants:

Его мнение о тебе неважное, но его можно исправить.

or

Его мнение о тебе неважное, и к тому же его нельзя исправить.

Come to think of it, I can construct sentences without «его» or «это»:

Его мнение о тебе неважное... но можно исправить!

But that sound like an omitted «это» (reference to whole situation), not the reuse of the noun like you thought. Also, that sounds like a flow of thought, like the speaker says the first part, thinks a bit, the exclaims the second part. That’s why I chose punctuation like this.

As for your «неважно и можно» examples, they sound like a mistake when I look at them as a separate sentence. Of course, it’s understandable what they try to say, so in a flow of text or speech I may not notice it. But when I have time to have a second look on the sentence, it sounds weird to me. Maybe in time such phrases would become common, but not yet.

Some of them can sound better if replaced with adjectives or participles:

• «не важно и можно пережить» to «не важно и преходяще»
• «не важно и можно исправить» to «не важно и исправимо»

Answer 2

One of my teachers once said that a noun in a sentence is always in a certain grammatical case and always has a certain role - the subject or an object. In other words, no noun can be in two different grammatical cases at the same time and play a dual role.

Your teachers are right.
Your examples does not prove, that one word can be used at dual function.

Его мнение о тебе неважно и к тому же можно исправить.

You think, that [к тому же можно исправить] is 100% about [его мнение], but this is not so.

In this case you just personally just mean it, but it does not follow from this pattern.

When you use it in just a chat - that's fine, but imagine, that someone would use this pattern in legal document, in papper agreement which has legal power. In this case, there are many options what exaclty you've ment as object in the second sentence.

For example, in the court you might say, that you've ment the following.

Его мнение о тебе неважно и к тому же всё можно исправить.

So, there is no rule, that if object is absent in the second part, then subject from the first part is meant.

Of course most people will think and understan, that you've ment [его мнение] as object, but it is not coming by rule.

The same effect is used in Japanese language.
You use kanji 一 for 1 and that goes everything all right.
But in legal documents they use kanji 壱 in order to guaranty 100% sure of what exactly was ment.

To be 100% sure from legal point in your case you have to say object excplicitly.

Его мнение о тебе неважно и к тому же его мнение можно исправить.
Его мнение о тебе неважно и к тому же такое мнение можно исправить.
Его мнение о тебе неважно и к тому же это мнение можно исправить.

If you do not put object explicitly by omtting the object you create field for assumtions.

Его мнение о тебе неважно и к тому же мужика можно исправить.
Его мнение о тебе неважно и к тому же всё можно исправить.
Его мнение о тебе неважно и к тому же стол можно исправить.
Его мнение о тебе неважно и к тому же документы можно исправить.
etc.

That means, that you can not say that [Его мнение] works in nominative and in accusative at the same time, because the second option is just omitted, but in full form object is availabe at the place.

The subject from the first part does not work in the second part.
It is just used for your imagination to guess what the omitted object is.

The more you ommit, the more there is possibility to misunderstand what you've ment.

Остальное неважно и можно выяснить потом.

Остальное неважно и отношения можно выяснить потом.
Остальное неважно и дела можно выяснить потом.
Остальное неважно и ответ можно выяснить потом.
Остальное неважно и его мотивы можно выяснить потом.
etc.

Остальное неважно и можно забыть.

Остальное неважно и об отпуске можно забыть.
Остальное неважно и об обиде можно забыть.
Остальное неважно и о его измене можно забыть.
Остальное неважно и о деньгах можно забыть.
Остальное неважно и о должности можно забыть. etc.

Пока ты любишь меня, все остальное неважно и можно пережить.

Пока ты любишь меня, все остальное неважно и развод можно пережить.
Пока ты любишь меня, все остальное неважно и пожар можно пережить.
Пока ты любишь меня, все остальное неважно и потерю можно пережить.
Пока ты любишь меня, все остальное неважно и этот дурдом можно пережить.
etc.

As you see, there is no 100% guaranty that the last part striclty uses the subject from the previous part, but of cource, people will understand what you've ment.

Summary

1. In 4 examples of yours you can not say, that subject works as object.
2. In fact, in every last sentence object is omitted (there is no object) and it is impossible to say with 100% guaranty what object was ment by the author of the text.
   Every option would be just a guess.
3. In common like that is not a problem.
   For legal text or for some serious buisiness or diplomatic letter that can be a problem.

Answer 3

In addition to the previous answers, I would like to point out that, although we native speakers always expect every noun in a well built sentence to be in a certain case, corresponding to its role in the sentence, the actual usage may differ, and it happens relatively often.

It does not even require the grammatical cases to have the same surface form. For instance,

«Победа» прекратила продажи билетов на международные рейсы из и в Санкт-Петербург... «Ведомости»

Here Санкт-Петербург is technically in Accusative, but it also serves as Genitive, required by the preposition из.

Шестнадцать? Четырнадцать? С или без Горация?.. (И. Бродский)

Such sentences can be analyzed as elliptical, i.e. «С [Горацием] или без Горация». However, it is obvious that this is not a typical ellipsis, since it depends on the context that first comes after it. For a listener it sounds more like a compound proposition (с-или-без) оr the noun Гораций factored out of enumeration, but none of these options quite follow the prescriptive rules of Russian.

Another example, written in a very formal register (a phrase from a contract)

... каждая заинтересованная сторона в отдельности может согласиться или отказаться от их использования... (Reverso)

Here the noun phrase «их использование» stands in Genetive, controlled by отказаться от, but also serves as Ablative, controlled by согласиться [с]. Unlike some similar sentences, this cannot be pragmatically analyzed as согласиться [со всеми условиями] или отказаться от их использования, so it must be either an untypical ellipsis, or a double control like in your examples. Or it may be a set phrase, originating in some old contract form.

To summarize, don't be very surprised when the word agreement in Russian does not work entirely as expected, there can be deviations like in any language. However, all such untypical sentences can be easily changed to follow the standard rules, and you better stick to those when you are talking or writing.