Case of complements in Russian

Question

Context: My book says that:

The copular verb is absent in the present tense for a compound predicate and the noun [which is the complement] is in the nominative case. In the past and future tenses there must be a copular verb быть (был, буду), стать (стал, стану).

Note that the above says nothing about which case the noun should be in for the past or future tenses. The book, however, gives the following examples of correct usage.

Мой брат -- журналист.
Мой брат был журналистом.
Мой брат будет журналистом.

Question 1: Does this mean that the following examples are incorrect?

Мой брат -- журналистом.
Мой брат был журналист.
Мой брат будет журналист.

/Question 1

I am pretty sure that the first sentence is incorrect, but I am not sure about the last two, because (1) I could have sworn I have seen sentences written with nominative in the past and future tenses, and (2) as mentioned above the book doesn't explicitly exclude the possibility of them being correct (in contrast to the first sentence, when it says that the noun must be in the nominative).

Question 2: When in general is the instrumental used with complements or copular verbs? Only in the past or future? Must it be used in those cases, or is it also correct to use nominative?

I am especially confused because I did not know that the instrumental could be used with быть or стать in any tense -- I thought it was only used for this meaning with the verb называться in very formal writing. /Question 2

Note: I translated the passage from my book from German, so it may not be entirely correct. In particular, it uses the grammatical term "Prädikatsnomen" which I am not sure how to translate, although this is mostly because the meaning of the word "predicate" in English is ambiguous.

predicate complement/ subject complement

Answer 1

Surprisingly, but - no! In a certain context, the first sentence is absolutely correct and is the only possible option. It can be used as a rhema-response (as opposed to a thema-response) to a topic question, e.g.

- Мой брат [topic] работает карманником. А твой [[кем] работает]?

- Мой брат - журналистом.

For the past tense, both был журналистом and был журналист are correct. The difference is that быть + Instrumentalis is similar to a past perfective form (as a perfective action unrelated to a moment of utterance), while быть + Nominative would be compared to a present-perfective structure in a language where such a distinction exists.

As for the future tense, some decades or a century ago the phrase with Nominative compliment [будет журналист] might be equally correct, but nowadays it sounds as a little bit obsolete.

The usage of Instrumental as a copular compliment is similar to that of Essive (a case of an impermanent state) in Balto-Fennic languages and can be regarded as a Fenno-Ugric substrate.

Answer 2

You are right. "Мой брат -- журналистом." is almost always incorrect and plain wrong.

One exception which I can think about is skipping words when a sentence is repeated:

- Твой брат стал журналистом.
- Мой брат -- журналистом?!

or

Я стал писателем, а мой брат -- журналистом.

Another one is a colloquial form expressing somebody's position: Я здесь начальником, я на этом сайте админом. You can also say in nominative: Я здесь начальник, я на этом сайте админ.

As for your general question, you may want to read the following: http://www.evartist.narod.ru/text1/62.htm#%D0%B7_02

Generally, with был/будет, nominative may be used for permanent feature, while instrumental is used for temporary feature. For example, if journalism was his life-long occupancy, you can both say он был журналист and он был журналистом. If he just worked as a journalist at the moment, you must say он был журналистом.

Another example (from the play "Тень" by Евгений Шварц):

Жила на свете стрекоза,
Она была кокетка.    <-- note the nominative of "кокетка"
Её прелестные глаза
Губили мух нередко.
Она любила повторять:
"Не стоит голову терять".

While the instrumental case (кокеткой) would still keep the meter and the rhyme, Schwartz used the nominative case, since "кокетка" was the permanent, even immanent, feature of the dragonfly.