When do you use "değil" & when do you use "yok"? I am confused. I've seen both.

Thanks!

In logic

not( not(X) ) = X

Turkish is logical language, so:

yok = there is not
yok değil = there is

para yok = there is no money
para yok değil = it is not that there is no money (=there is money)

In addition,

They both mean no, nope, not, ain't. (Informal)

For example:

-Dün işe gittin mi? (Did you go to work yesterday?)
-Yok, gitmedim. (Nope, I didn't.)

-Sen bu işleri yapacaksın, değil mi? (You will do these works, won't you?)
-Değil, ben yapmayacağım. (No, I won't do them.)

By the way, usage of "yok" is more common. And people also say "yo" to give the meaning of "no", of course it is informal too

I follow Delidolu on this. I will expand on her post, with apologies.

"Değil" is used to negate a statement.

To say: "Hatice is pretty.", you'd use: "Hatice guzel."

To say: "Hatice is not pretty.", you'd use: "Hatice guzel değil."

"Yok" is the opposite of "var", "exist, in existence".

To ask: "Is there fruit?", you'd use: "Meyveler var mı?". Literally, this means something like: "Fruits in existence are there?"

The reply: "Meyveler yok." literally means "Fruits not in existence."

So the key is to know whether "var" would be used in the opposite (positive) statement. If "var" would be used, replace it with "yok". Otherwise, state the positive statement, then attach "değil" to form the negative.

95% of the time, it is easy to decide which to use. The var/yok system is very basic to understanding Turkish, to actually begin to think in Turkish. Once you get the hang of it, it comes out spontaneously.

"Değil" is more like "not" in English, in particular the recent sarcastic usage, for instance: "Dave is a handsome guy. Not!"

"Değil", of course, doesn't carry any sarcasm.