When to use "бы"?

Question

is it true that бы replace the use of "would" or "would've" in English? someone told me that and give me those examples:

I would've done it = я бы хотел это делать

I would like to read = я бы хотел читать

is that true?

Answer 1

is it true that бы replace the use of "would" or "would've" in English?

Generally speaking, this statement is incorrect.

The particle бы and its short form б are used to speak about something hypothetical, so sometimes it can have the meaning of "would" and "would have" but generally they have the meaning of English constructs which use verbs in their corresponding past tense to describe something hypothetical or in a more polite way.

Like:

• If I were you, I would be happy Если б(ы) я был тобой, я был бы счастлив. Here you can see two instances of бы and they are presented as the past and future in the past tense of be: were and would be

• I could have done this before. Я б(ы) мог это сделать раньше. Here once again you can see the occurrence of бы or б and no "would" or "would have".

• Could you give me a pen? Могли бы вы дать мне ручку? Here we have бы exactly with the same meaning which "could" has opposed to "can" in English. This is a more polite way to ask something.

Also these letter combinations бы and a single б can be heard in the conjunctions чтобы and чтоб. In spoken language they can be misunderstood as the standalone particles бы and б.

• In order to be healthy one should work out. Чтобы быть здоровым, надо заниматься физкультурой. or I have decided to do it today so that I can rest tomorrow. Я решил сделать это сегодня, чтоб отдыхать завтра. They are used to combine the secondary part of a sentence (which passes info about a purpose of something or that something is desirable, acceptable etc.) and its main part

I would've done it = я бы хотел это делать

This translation is incorrect. It means Я бы это сделал. There is nothing about "to want" (хотеть, хотел - the past form)

Answer 2

It is not (always) true. Mainly because proper translation is expressing the same sense by means of another language, so generally, it can't be limited to replacing words. For example, in English 'would' can be used to express repeated (usual) action of main verb in the past, and the Russian version of that never takes бы. A quote from a book:

When I was 8, my father would come home in the evening and I would always be sitting, waiting, in my numbered shirt and baseball cap.

(Когда мне было 8 лет, отец [обычно, бывало] приходил домой вечером, а я всегда сидел и ждал его в майке с номером и бейсболке.)

As for your examples. The second one is about correct in translation (maybe "я хотел бы заняться чтением" would sound more natural). The first one expresses unused possibility to complete an action in the past (not a desire to do smth. in nearest future) and needs a perfective verb in Russian:

I would've done it = я бы (уже) это сделал

Answer 3

Бы generally is for subjunctive (or conjunctive? google tells both for сослагательное наклонение) mood.

Я бы предпочёл не проводить остаток зимы привязанным к сраному дивану. (http://www.youtube.com/watch?v=XufZexZc-n0)

I do - я делаю, I would do - я бы сделал.