si for commencing a question.

[chandan Bhatnagar]

hi,
we often use "if" in english for starting a question.
eg. if you know him?
if you are finished ?

i wrote a sentence 《si tu aimes qqn ?》
which my teacher corrected to 《 est-ce que tu aime qqn ?》

why? why《 est-ce que》 is prefered here than 《si》

[George Hunt]

I am not quite sure  how you are using  "if" .Do  you want to give a bit more of the context? (in the English I mean.) 

[chandan Bhatnagar]

i wanted to write "if you love somebody" as a general question..

[Charles D]

"If" in English never begins a question when it stands alone.  "If you love somebody?" is not a proper question in English.  At best, it is a fragment leading to an implied question that the listener would mentally fill in.

Here's an example:

Bill: I could never do that.

Tom: If you love somebody? (If you love somebody, could you do that?)

Bill: If I loved somebody, yes. (If I loved somebody, yes, I could do that)

The italicized sentences are what is implied.  In English we truncate out interchanges often through implication that is understood in the context of the exchange.

You are trying to translate this implied speech into French by thinking like an English speaker.  The trick is to think like a French speaker.  Many of us on this site are not proficient enough in French colloquial constructions to be able to do that.  We all have to stay in the classroom a little longer, as it were.  

[Chantal Savignat]

These implied ways are possible in French too. With the same way !  (sometimes, by chance it's right). But only in an oral discussion and the context must be known. Writing only the question with "if" makes no sense.

Your exemple is correct in French too :

Bill: Je ne pourrais jamais faire ça.

Tom: Si tu aimes quelqu'un ?  => an other way sounds better (and is more used). We would rather say    "Même si tu aimes quelqu'un ?"

Bill: Si j'aime quelqu'un, oui.

[Charles D]

Merci, Chantal, pour votre réponse.  

[Chantal Savignat]

Hello

In French a question never begins with "si".

"Si tu aimes quelqu'un" = "if you love somebody" is a general affirmation (condition) and is written without "?" at the end of the sentence. This sentence in French can't be understood as a question.