EN OR A LA MESA?

Mankind invented language to communicate, not to create confusion. Languages with prepositions -Spanish, and English- have problems with usage. Native speakers sometimes have problems with prepositions and ideas are not forwarded clearly. In English, there is a clear distinction between "Johnny is sitting on the table" and "Johnny is sitting at the table". Likewise, in Spanish we say "Juanito está sentado en la mesa" and "Juanito está sentado a la mesa." In both examples, where Johnny is situated regarding the table is clear. But enter Spaniards and start confusing "en" with "a" in this case and "Johnny está sentado en la mesa" may now mean "sitting at the table or sitting on the table." This silly confusion has led the Spanish Language Academy (Real Academia Española) to sanctify and sanction the error and accept it as good. The result is that when someone tells us that "Juanito está sentado en la mesa" we do not really know where Juanito is, whether near (at) or on top of it (on).