I'm trying to understand when you are commanding something, when you change the verb ending and when you don't. As I understand it, when you are telling someone to do something instead of asking, you use the formal usted version of the verb, and you change an AR verb into an ER verb, or an ER/IR verb into an AR verb. Some examples:
Volver - "Vuelva a las ocho!", not "Vuelve a las ocho!"
Trabajar - "Trabaje más rápido!", not "Trabaja más rápido"

I'm also seeing that some verbs don't change, such as hablar, abrir, and cerrar. You would use "habla, abre, and cierra" instead of "hable, abra, and cierre". Why is that? Why are some verbs changed and some not changed? What percentage of all the verbs in existence are changed versus verbs that aren't changed when using a command? 50-50? Any more examples of ones that change and ones that don't would be appreciated.

When I ask native Spanish speakers that I know personally, they say they just know when they say or hear it if it sounds weird. That doesn't help me

Question

I'm trying to understand when you are commanding something, when you change the verb ending and when you don't. As I understand it, when you are telling someone to do something instead of asking, you use the formal usted version of the verb, and you change an AR verb into an ER verb, or an ER/IR verb into an AR verb. Some examples:
Volver - "Vuelva a las ocho!", not "Vuelve a las ocho!"
Trabajar - "Trabaje más rápido!", not "Trabaja más rápido"

I'm also seeing that some verbs don't change, such as hablar, abrir, and cerrar. You would use "habla, abre, and cierra" instead of "hable, abra, and cierre". Why is that? Why are some verbs changed and some not changed? What percentage of all the verbs in existence are changed versus verbs that aren't changed when using a command? 50-50? Any more examples of ones that change and ones that don't would be appreciated.

When I ask native Spanish speakers that I know personally, they say they just know when they say or hear it if it sounds weird. That doesn't help me

betto007 · Answer

@cfouse About "when you are telling someone to do something instead of asking", at grammar level there is no difference in Spanish because all of that is the imperative mode for a verb. It doesn't really matter if you are giving a command or kindly asking for something, there is only one mode: imperative. What you may have heard is the different way to do the imperative mode when it's said in casual way versus formal way for the 2nd personal pronoun, this is, "Tú" (informal) and "Usted" (formal). That being said, here are some examples:

Imperative formal
- (Usted*), siga caminando en línea recta
(Keep walking straight ahead)
*"usted" it's commonly omitted

Imperative informal
- (Tú), sigue caminando en línea recta
(Keep walking straight ahead)

Another examples with conjugation for verbs in imperative mode for Usted(formal) vs Tú(informal):

Comer -> To eat
- ¡Come toda la comida!(informal)
- ¡Coma toda la comida!(formal)
[Eat all your food!]

Pagar -> To pay
- ¡Paga lo que me debes!(informal)
- ¡Pague lo que me debe!(formal)
[Pay what you owe me!]

Sonreír -> To smile
- ¡Sonríe, por favor!(informal)
- ¡Sonría, por favor!(formal)
[Smile, please!]

cosmostitan · Answer

Ambas formas, la formal y la informal, pueden ser usadas para dar una orden y ninguna de estas formas se usa para preguntar. Usas la forma formal (usted) cuando le das una orden a alguien que no conoces, que no le tienes mucha confianza, o que tiene mayor gerarquia que tu. Usas la forma informal (tu) cuando le das una orden a alguien a quien le tienes confianza porque es cercano a ti por ejemplo un amigo o un familiar que tiene igual o menor gerarquia que tu.