In Spanish, the endings of the conjugated verbs marks the person.
Sólo comemos vegetales y verduras.
We only eat vegetables and greens.
Somos vegetarianos. (Nosotros)*
We are vegetarians.
Fui a llevar las cartas a la oficina de correos. (Yo)
I went to take the letters to the post office.
Tienen muchas ganas de comer paella (Ellos/Ellas)*
They really want to eat paella.
That is the reason why it is not necessary to always put the subject pronoun, although there are three situations in which we cannot get rid off the subject pronoun.
Situations:
A.- When the first ("Yo") and third ("Él/Ella/Usted") singular person are the same. This always happens in the Imperfect and Conditional. We need the subject pronoun to know who we are talking about and avoid the confussion.
Examples:
Cantaba en el coro de la iglesia - INCORRECT
I/he/she/it sang in the church choir
Él cantaba en el coro de la iglesia -or- Yo cantaba en el coro de la iglesia - CORRECT
He sang in the church choir -or- I sang in the church choir
Podría ayudarte con tus deberes de física - INCORRECT
I/he/she/it could help you with your physics homework
Él podría ayudarte con tus deberes de física -or- Yo podría ayudarte con tus deberes de física - CORRECT
He could help you with your physics homework -or- I could help you with your physics homework
B.- When two people talk, one says something and the other wants to contrast that thing.
Person A: No tengo ganas de ir a la fiesta esta noche.
Person A: I don't feel like going to the party tonight.
Person B: Pues yo sí que tengo ganas de ir a la fiesta.
Person B: Well I do feel like going to the party.
Person A: He engordado cuatro kilos desde que dejé de ir al gimnasio.
Person A: I've gained four kilos since I stopped going to the gym.
Person B: Pues yo he engordado tres kilos desde que dejé de ir.
Person B: Well I've gained three kilos since I stopped going.
C.- When we emphasize the person performing or not an action.
Person A: ¿Vas a contarle a tu madre lo de tus notas?
Person A: Are you going to tell your mother about your grades?
Person B: Cuéntaselo tú, porque yo no me atrevo.
Person B: You tell her, because I don't dare.
Person A: Mario dice si puedes ir a la cocina y traerle un vaso de agua.
Person A: Mario says if you can go to the kitchen and get him a glass of water.
Person B: Que vaya él, porque yo no quiero nada.
Person B: Let him go, because I don't want anything.
* Note: When the pronouns have masculine and femenine forms (él/ella, nosotros/nosotras,vosotros/vosotras, ellos/ellas) there must be a previous mention of the gender in the sentence, or and adjective in the sentence that specifies the gender.
Somos vegetarianos. (Nosotros)
Somos vegetarianas. (Nosotras)
Tienen muchas ganas de comer paella (Ellos/Ellas) --> we need a previous context to identify the gender of the pronoun subject
Remember that the masculine pronouns are used to define a mixed group of people.
Tienen muchas ganas de comer paella (Ellos) --> even if "they" refers to man and woman at the same time.
Sólo comemos vegetales y verduras.
We only eat vegetables and greens.
Somos vegetarianos. (Nosotros)*
We are vegetarians.
Fui a llevar las cartas a la oficina de correos. (Yo)
I went to take the letters to the post office.
Tienen muchas ganas de comer paella (Ellos/Ellas)*
They really want to eat paella.
That is the reason why it is not necessary to always put the subject pronoun, although there are three situations in which we cannot get rid off the subject pronoun.
Situations:
A.- When the first ("Yo") and third ("Él/Ella/Usted") singular person are the same. This always happens in the Imperfect and Conditional. We need the subject pronoun to know who we are talking about and avoid the confussion.
Examples:
Verb CANTAR | ||||
| Imperfect | Conditional | |||
| Yo | cantaba | Yo | cantaría | |
| Tú | cantabas | Tú | cantarías | |
| Él/Ella/Usted | cantaba | Él/Ella/Usted | cantaría | |
Cantaba en el coro de la iglesia - INCORRECT
I/he/she/it sang in the church choir
Él cantaba en el coro de la iglesia -or- Yo cantaba en el coro de la iglesia - CORRECT
He sang in the church choir -or- I sang in the church choir
Verb PODER | ||||
| Imperfect | Conditional | |||
| Yo | podía | Yo | podría | |
| Tú | podías | Tú | podrías | |
| Él/Ella/Usted | podía | Él/Ella/Usted | podría | |
Podría ayudarte con tus deberes de física - INCORRECT
I/he/she/it could help you with your physics homework
Él podría ayudarte con tus deberes de física -or- Yo podría ayudarte con tus deberes de física - CORRECT
He could help you with your physics homework -or- I could help you with your physics homework
B.- When two people talk, one says something and the other wants to contrast that thing.
Person A: No tengo ganas de ir a la fiesta esta noche.
Person A: I don't feel like going to the party tonight.
Person B: Pues yo sí que tengo ganas de ir a la fiesta.
Person B: Well I do feel like going to the party.
Person A: He engordado cuatro kilos desde que dejé de ir al gimnasio.
Person A: I've gained four kilos since I stopped going to the gym.
Person B: Pues yo he engordado tres kilos desde que dejé de ir.
Person B: Well I've gained three kilos since I stopped going.
C.- When we emphasize the person performing or not an action.
Person A: ¿Vas a contarle a tu madre lo de tus notas?
Person A: Are you going to tell your mother about your grades?
Person B: Cuéntaselo tú, porque yo no me atrevo.
Person B: You tell her, because I don't dare.
Person A: Mario dice si puedes ir a la cocina y traerle un vaso de agua.
Person A: Mario says if you can go to the kitchen and get him a glass of water.
Person B: Que vaya él, porque yo no quiero nada.
Person B: Let him go, because I don't want anything.
* Note: When the pronouns have masculine and femenine forms (él/ella, nosotros/nosotras,vosotros/vosotras, ellos/ellas) there must be a previous mention of the gender in the sentence, or and adjective in the sentence that specifies the gender.
Somos vegetarianos. (Nosotros)
Somos vegetarianas. (Nosotras)
Tienen muchas ganas de comer paella (Ellos/Ellas) --> we need a previous context to identify the gender of the pronoun subject
Remember that the masculine pronouns are used to define a mixed group of people.
Tienen muchas ganas de comer paella (Ellos) --> even if "they" refers to man and woman at the same time.