The verb "ser" is one of two primary verbs in Spanish that mean "to be," the other being "estar." "Ser" is used to express the identity, characteristics, and origin of subjects, as well as time and possession. The sentences provided are using "ser" for the following reasons:
1. ¿De dónde eres? (Origin)
- This question asks "Where are you from?" The verb "ser" is used here to inquire about the origin or nationality of a person, which is a permanent characteristic.
2. La chica es alta. (Characteristic)
- This statement translates to "The girl is tall." Here, "ser" expresses a characteristic of the girl. Characteristics such as height, personality, and physical attributes that are generally stable and inherent to an individual are usually described with "ser."
3. ¿Qué día es? (Date)
- This question means "What day is it?" "Ser" is used to talk about the date and time since these are perceived as fixed or defining properties of a day or moment.
Each usage aligns with the general rules for when to use "ser" as opposed to "estar." "Ser" is typically used for descriptions that are considered permanent or defining, whereas "estar" is used for states or conditions that are temporary or changeable.