Putting LUI and Y together

Why would it be correct to put LUI and Y together? Grammatically, I think this follows the rules but it sounds so unnatural. Is this really done in everyday French? Examples: “On lui y cherche un livre.” “Il lui y prete des outils” 

Hi JennyBBien,

Great question—and you're absolutely right to notice that lui and y together sound awkward, even if grammatically it might seem possible.

Is it grammatically correct?

Technically, French grammar allows lui (an indirect object pronoun) and y (a pronoun that replaces a place or a thing introduced by à) to appear together in a specific order:
me/te/se/nous/vous → le/la/les → lui/leur → y → en.

So yes, in theory, you can have lui y together, like in:
On lui y cherche un livre.

But…

Is it actually used in everyday French?

No, not really.
Even though it follows the grammatical order, native speakers almost never say things like lui y because it’s clunky and confusing to follow in real time. In speech, it sounds unnatural and is avoided.

Instead, French speakers will rephrase the sentence to avoid stacking pronouns like that. For example:

Instead of On lui y cherche un livre you'd hear something like:
On cherche un livre pour lui là-bas.

Instead of Il lui y prête des outils, you’d hear:
Il prête des outils à Luc dans le garage or Il lui prête des outils là-bas depending on context.

Native speakers instinctively reword or separate the ideas to make them clearer and more natural. 

I hope this helps!