No se lo digas a Juan - why is se necessary?

Question

I just asked my (Spanish) girlfriend how to say "Don't tell Juan". She explained to me that the translation is "No se lo digas a Juan" but she's wasn't able to clearly explain why the "se" was necessary.

Would anyone be so kind as to break this sentence down for me and explain why "No lo digas a Juan" cannot be used?

Thanks!

Welcome to spanishdict. We ask that all new members complete their profiles with their native language, and what level of Spanish you feel you are, like, beginner, intermediate, etc. as well as gender. - ray76, Oct 15, 2016

Answer 1

"No lo digas a Juan" is ungrammatical. Even though you say "a Juan," the indirect object pronoun is required. That pronoun would be the third-person singular le, but we don't say le lo digas -- we change le to se.

See here and here.

Thanks @jtaniel, that makes sense. A classic use of "se" whenever things simply don't sound right! - lcooperdesign, Oct 14, 2016

I tell my students that "le lo" sounds too Hawaiian. :) - Daniela2041, Oct 14, 2016

On the other hand, "le la" got me on my knees. - jtaniel, Oct 16, 2016

thaaaanks brother. much appreciation. - Yasser7102, Aug 23, 2017