Both these words can translate as if, yet their usage is uniquely different.
How do these two words differ?
The answer may seem complicated at first, however, with some practice, you’ll manage to use both words flawlessly.
| если [if] |
There’s a lot more I could say about если than what we will see here. That being said, I think it’s best to keep things brief on its usage for this post.
| Если ты так думаешь, то я ошибся. If that’s what you think, then I was wrong. |
| Если она замужем, то лучше к ней не приставать. If she’s married, then you’d best not bother her. |
| Если на улице прекрасно и солнечно, то мы ходим по городе. If it’s nice and sunny outside, then we walk around the city. |
| The typical construction, if the sentence starts with если, is если…, то… The usage of то however is optional. |
Because you can have если in the middle of a sentence.
| Я поеду в Швейцарую, если у меня будет достаточно денег. I will go to Switzerland if I have enough money. |
| Она будет очень сердита, если ты провалишь экзамен. She’ll be very mad if you fail the exam. |
| ли [whether, if] |
The word ли is tricky to explain. It has additional meanings, but we’ll only be focusing on its usage with if, whether.
If you use a verb or collocation related to receiving information such as спрашивать [to ask], знать [to know], мне интересно [I wonder], я не уверен [I’m not sure], etc.
| Pay attention to the word order! The information in question goes directly after the verb and is followed by ли. This will take some practice to get used to. |
| Рома спрашивает, знаю ли я пароль. Roma asks if I know the password. |
| Рома спрашивает, пароль ли я знаю. Roma asks if the password is what I know. |
| Рома спрашивает, я ли знаю пароль. Roma asks if it’s me who knows the password. |
It can be used with или [or].
| Я не уверен, учится ли она или работает. I don’t know whether she studies or works. |
| Я не знаю, по-русски ли говорит она или по-украински. I don’t know whether it’s Russian or Ukrainian that she speaks. |
Because of this, in addition to translating as if, it can also translate as whether.
My Slavic Studies 