I saw this ad from the Rio Tinto Alcan Planetarium in Montréal. It reads:
T’es vraiment dans la Lune!
The expression être dans la lune means to be out to lunch, to not be with it, to have your head in the clouds, etc. This expression works well in an ad from a planetarium because it contains the word lune.
There’s an informal usage in the ad, which is t’es (sounds like té). This is a contraction of tu es, and it’s used very frequently in spoken language.
The authors could’ve put in a second informal usage in the ad, but they chose not to. Do you know what informal usage that might be?
Maybe you’ll remember that when dans and la come together, they can give rise to an informal contraction: dans’.
This means tu es dans la lune can be pronounced informally as t’es dans’ lune.
Why then didn’t they put the informal dans’ in the ad if they were willing to use t’es? It isn’t unusual to come across t’es in advertising, but dans’… very rare. The authors probably felt dans’ would’ve rendered the text too informal, striking readers as inappropriate.
Maybe we can compare it to the informal yer and gonna in English. You might come across you’re gonna love it in an ad, with the informal gonna, but you’re much less likely to come across yer gonna love it, even though that’s how you’d pronounce it spontaneously.