A friend from Central America was reading a Montréal newspaper article and came across an expression he didn’t know:
C’est-y pas beau?
He asked what this expression means and what the y is doing in there.
Here’s an example context (that I’ve made up) of how the expression was used:
Le gouvernement va augmenter la taxe sur l’essence. C’est-y pas beau, ça?
The government is going to increase tax on gas. Well ain’t that nice?
Can you guess now what that y means? It means the exact same thing as tu when used informally to create a yes-no question.
C’est vraiment necessaire.
C’est-tu vraiment necessaire?
It’s really necessary.
Is it really necessary?
C’est ben cher.
C’est-tu ben cher?
It’s really expensive.
Is it really expensive?
Y and tu, when used to create informal yes-no questions, are variants of one another.
The question c’est-y pas beau? contains sarcasm. The person asking this question dislikes the situation it refers to and is using the question to highlight this fact.
I assume that liaison is used here and the t is pronounced?
Yes, the t is pronounced. What’s more is that because the t comes before an i sound, it gets pronounced ts, like the ts in the English word cats. So c’est-y sounds like cé tsi. Similarly, c’est-tu sounds like cé tsu because t also sounds like ts when it comes before the u sound.
Are y and tu for informal yes-no questions always interchangeable or are there certain cases where you can only use one or the other?
They’re interchangeable, but tu is by far the preferred form in spoken language in Montréal. The y form is heard in rural France and Acadie (if I’m not mistaken).