Thread: Это

1. The verb "быть" (to be) is not a transitive verb! And "мужчина" is not an object! "To be" (both in English and in Russian) is a copula verb. And what comes after "to be" is grammatically a predicate.

2. The present tense of "быть" is rarely used in modern Russian. But if you decide to use it, it should be "есть", not "быть". "Быть" is infinitive (to be), "есть" is its present tense (am/is/are). So, not "я быть мужчина", but "я есть мужчина". But in 99% of cases you do not need this form.

3. In past and future there is a tricky thing with "to be" in Russian. You can keep the predicate in nominative:
"Я был мужчина", "Я буду мужчина".
But it is more natural to put it in instrumental:
"Я был мужчиной", "Я буду мужчиной".

This only works in past and future (not in present)! It is hard to explain why, but you may think of it as if you were describing a role:
"I played a role of a man", "I will play a role of a man". When describing a role, we use instrumental:
"Он работает врачом" - "He works as a doctor".

ShakeyX, may I give some advice to you?

The questions you ask are good questions, they are "deeply thought" (BTW, is there such an expression in English)?
But they relate to the very basics of the Russian grammar, and any good grammar book surely explains everything of this stuff.

You are welcome to ask your questions in the forum, but I would advise you to find a Russian reference grammar book. There should be a rich choice of them!