Origin of the "le to se"change?

Question

One of the things that I do regularly is search through my Spanish notes and textbooks and go through the rules and concepts to continue with practicing. Every time that I do this, I always come across this letter to a friend of mine, from his brother. His brother was a translation major and my friend was living in Spain at the time that he received this letter. I no longer have contact with either of these two fellows, but I still have the letter which contained some grammar lessons about direct, indirect and combined object pronouns.

Una de las cosas que hago semanalmente es escudriñar las notas y los libros de texto acerca de las reglas y los conceptos de la lengua española para seguir practicando. Cada vez que lo he hecho, he leído una carta, mandada a un amigo mío por su hermano. Su hermano era un estudiante meticuloso acerca de la traducción entre español e inglés y mi amigo estaba viviendo en España cuando él recibió esta carta. No he tenido contacto con ellos por mucho tiempo, pero tengo la carta todavía de lo que tiene lecciones gramáticas acerca de los pronombres de objeto directo, indirecto y combinado.

Finally, to get to the point of the question here, the letter states somethings along these lines:

Para llegar al fin de esta cuestión, la carta dice algo así:

"There are quite a few people out there that believe the "le to se" change came into existence in order to avoid the double pronunciation of "le lo". However, this would not be the case. From the education that I've received, this rule actually comes from Latin. Sadly, you don't know enough about Latin for me to give you the rundown on the origin of this change and I don't have the time to do that. Just know, that if anyone asks you about where this grammar rule came from, it's originally from Latin."

"Hay bastante personas que creen que el cambio de "le a se" vino para evitar la pronunciación incómoda de "le lo". Sin embargo, este no es el caso. Por causa de la educación que he recibido, esta regla, en verdad, vino del idioma latín. Pues, no sabes bastante acerca de latín para que yo te pueda explicar el origen de este cambio, y no tengo el tiempo para hacer lo mismo. Si alguien te pregunta acerca de dónde vino esta regla gramatical, sabe que vino de latín."

So, the question is, does anyone know where this rule came from? And/or does anyone know if what this man has said about the origin of the rule is true and what the rule might be called at an academic level?

Entonces, la pregunta es, ¿sabe alguien el origen de esta regla? Además, ¿sabe alguien si las cosas que este hombre ha dicho acerca del origen de esta regla son verdaderas? Y ¿cómo se llama esta regla?

Thanks - rac1, Oct 10, 2016

Answer 1

I had always heard it was a phonetic issue, to avoid double pronunciation of "under him."

I had heard that as well, until I had read this letter. The grammar notes that I received from my friend's brother have yet to lie to me. - codyandrews1993, Oct 10, 2016

Thanks Luis. - rac1, Oct 10, 2016