"To be, or not to be?" was Hamlet's perplexing question. The Spanish student must grapple with a similar one: "Which 'to be' to use?"
There are several instances in Spanish where one English word (or tense) can be translated two different ways in Spanish (Por and Para, The Imperfect Tense and the Preterite Tense, Ser and Estar) and the decision you make can have an impact on the meaning of the sentence. Translating from Spanish to English is not a problem because both ser and estar become a form of "to be." Translating from English to Spanish on the other hand is much more difficult because a decision needs to be made on which of the two words to use.
Before we get too much further, let's take a quick look at the (present tense) conjugations of both verbs:
Ser is completely irregular, and estar has an irregular yo form along with accented endings in all but the nosotros and vosotros forms.
Ser and Estar: The Basics
So how do we decide which verb to use? Here's when we use estar:
When to Use Estar
"To say how you feel and where you are, you should use the verb estar."
An easy way to think about the verb estar is that it is used to describe temporary conditions and locations. Conditions can be mental, emotional, or physical states of people, animals, and objects. Locations are quite simply where something or someone is.
Pepe y Pablo están en mi dormitorio.
Emilia está enferma.
Note: Because estar is associated with location, words like "here" or "there" are optional: Jaime no está. (Jaime isn't here.)
"Pepe and Pablo are in my room." This sentence describes someone's location so están (not son) is used. "Emilia is sick." This sentence is talking about Emilia's physical condition so está (not es) is used.
In both of these situations the condition mentioned is temporary. Presumably Pepe and Pablo won't always be in my room; hopefully Emilia won't always be sick.
On the other hand...
When to Use Ser
Since estar deals with temporary conditions, that leaves ser as the verb to use for more permanent situations. Generally speaking, ser is used when dealing with "inherent characteristics." That's a fancy way of saying things which are not likely to change.
Mi coche es amarillo.
Sus hermanos son muy delgados.
"My car is yellow." This is not likely to change. The car probably has been yellow for some time and will continue to be yellow into the future. We wouldn't expect it to suddenly be another color tomorrow. "Her brothers are very thin." Again, this is a state that we wouldn't expect to change quickly. When we think of these brothers, we think of them as being thin and don't expect them to rapidly put on weight.
Notice that in these examples it's not impossible that the characteristics would change (cars are repainted all the time, and thin people sometimes get bigger). It's just unlikely to expect that they would soon.
The Exception: Events
It wouldn't be a rule if it didn't have an exception, right? In spite of the fact that it deals with a location, we use ser rather than estar to talk about where and when events will take place.
La fiesta es en la casa de Alejandro.
Los partidos de futbol son en el estadio.
"The party is at Alejandro's house." "The soccer games are at the stadium." Both of these situations might feel like we should be using a form of estar since we're dealing with where these things are happening, but we use ser with events. Think of ser as meaning "to take place."
Ser and Estar: Differences in Meaning
Your choice of using either estar or ser can also have an impact on the rest of the sentence. Certain adjectives will convey different meanings based on which verb they're paired with:
La manzana es verde.
La manzana está verde.
The first sentence uses ser so we're talking about an inherent characteristic of the apple. It should be translated, "The apple is green," meaning simply that the color of the apple is green. The second sentence uses estar so we're dealing with its current condition. This sentence should be translated something along the lines of, "The apple is not ripe," meaning that it still needs to ripen up and turn red. Another example:
¿Cómo eres tú?
¿Cómo estás tú?
Both of these sentences could be translated exactly the same way in English, "How are you?" However, since the first sentence uses a form or ser, the implied question is not "How are you right now?" but "How are you usually?" or better yet, "What are you like?" The second question is the more familiar "How are you?" or "How are you doing?"
Some other examples:
I am tired. (now)
I am a tired person.
You can use the differences between ser and estar to comment on changes from what you consider normal.
Los coches son muy caros.
Cars are very expensive. (They are usually expensive.)
Los coches están muy caros.
Cars are very expensive. (They are especially expensive right now.)
Marisól es delgada.
Marisól is thin. (She is normally a thin person.)
Marisól está delgada.
Marisól is thin. (She has lost weight recently.)
Ser and Estar: Other Uses
Use estar in present progressive and imperfect progressive conjugations:
¡Yo te estoy hablando!
Ella estaba llamándome.
Time, Days, and Dates
Use ser when talking about the time, days, and dates:
¿Qué hora es? Son las diez.
Hoy es sábado. Hoy es el 29 de septiembre.
Use ser when talking about possession:
El coche es de Pancho.
El sombrero es del Sr. Fajardo.
Use ser when talking about occupation:
¿Qué eres tú, Manuel? Soy abogado.
Use ser when talking about origin:
Marta es de Honduras.
¿Estas camisas son de Guatemala?
Use ser when talking about material used:
Mis anillos son de oro.
Estas cajas son de cartón.
Use ser in passive voice constructions:
Tres casas son construidas cada semana.
La puerta fue cerrada por el viento.
Use ser in impersonal expressions:
Es importante estudiar.
Es difícil estudiar con tanto ruido.
All of the present tense ser and estar rules apply to other tenses as well:
Yo estaba muy enfermo.
La boda será en la catedral.
¿Qué hora era?
Knowing Whether to Use Ser or Estar
Perhaps the most difficult part about using the Spanish verbs ser and estar correctly is choosing which one to use. When you encounter different types of being — unchanging essential being and being that changes depending on various conditions — trying to pigeonhole them as one or the other can be quite challenging.
Deciding when to use ser
You use the verb ser to describe the unchanging characteristics of a person, place, or thing, but what exactly does that mean? The following lists provide additional details to help you identify situations in which to use ser:
Origin and Nationality
Ella es de España. (She is from Spain.)
Ella es española. (She is Spanish.)
The Four P’s: Personality, Physical Attributes, Profession, and Possession
Él es divertido. (He is fun.)
Susana es baja. (Susana is short.)
Mi padre es un médico. (My father is a doctor.)
El carro azul es mío. (The blue car is mine.)
Date and Time
Hoy es el seis de enero. (Today is January 6th [the 6th of January].)
Son las nueve de la noche. (It is 9 p.m.)
Ellos son mis padres. (They are my parents.)
Rafael es mi mejor amigo. (Rafael is my best friend.)
Deciding when to use estar
You use the verb estar to describe the changing characteristics of a person, place, or thing, but figuring out when that rule applies can be easier said than done. The following lists help you know when to use estar:
Su casa está en la avenida Juárez. (Her house is on Juarez Avenue.)
El cine está cerca del centro. (The cinema is near the center of town.)
Mood and Physical Condition
El profesor está enojado. (The teacher is angry.)
Mi madre está emocionada. (My mother is excited.)
Los estudiantes están aburridos. (The students are bored.)
La señorita Martínez está enferma. (Miss Martinez is sick.)
Result of an Action
Los niños están de pie. (The children are standing.)
La audiencia está sentada. (The audience is seated.)