Spanish names

[i d unknown]

When mentioning the name of someone you are not familiar with in conversation would you use the full name more than once?

For example: You first mention: Luis de Rojas y Mendoza.

Would you refer to him again as Luis de Rojas y Mendoza.

or Luis de Rojas.

or de Rojas.

or Luis y Mendoza.

or y Mendoza.

or de Rojas y Mendoza?

[AngelicaDeAlquezar]

This topic is not complex, but it depends on a few things.

In general, we use two family names (father's family name and mother's family name) with our first name.
Let's say we have Juan José Hernández Pérez. "Hernández" is Juan José's father's family name and "Pérez" is his mother's family name.
A formal way to shorten his name will be "Juan (José) Hernández", if we have to make sure everyone knows whom we're talking about.
If we talk about this person and we already mentioned his name, we can say just "Hernández"
- El autor Juan José Hernández Pérez es el autor de este libro. Hernández también es músico...

In your example, I assume the father's family name is "de Rojas" and the mother's family name is "Mendoza".
In this case, we would shorten his name to "Luis de Rojas", and when talking about him where everyone knows who he is, we'll say "De Rojas".

"Y Mendoza" doesn't make much sense, because "y" is not really a part of the last name, but rather an addition to distinguish both family names.

As for "Mendoza" alone, it's unusual to talk about someone by their mother's family name, because it's considered impolite. However, if it's an uncommon name in comparison with his father's family name, then many people will tend to talk about him by his mother's name. An example of this is former Mexican President, "López Obrador"; people refer to him as "Obrador", because "López" is too commonly heard, but "Obrador" isn't, so people remember this last name more easily.

We would use "De Rojas y Mendoza" if this were his father's last name as a whole. In that case, there should be a "third" family name, which would be his mother's. (Let's say his name is Luis de Rojas y Mendoza Martínez.)

[i d unknown]

Thank you.