This topic often is one of most difficult things to learn and understand about Spanish (probably together with subjunctive). Many languages use only one verb to describe what we do with two. It is not difficult to go from two verbs to one but it is definitively a challenge to understand fully the different meanings of ser and estar. This part will be only a small introduction and basic conjugation of both verbs which we use everyday in many sentences.
Main function of verb ‘estar’ is to attribute to the subject an specific characteristic or state, function that also is done by the verb ‘ser’.
On one hand, verb ‘estar’ is generally used when the characteristic that is attributed to the subject, is considered as a result of an action, transformation or change, real or supposed, or not considered as permanent, meaning that it is linked to a temporal situation. On the other hand, when the characteristic that is attributed to the subject, is considered as inherent or stable to this person, or presents the characteristic without being attached to some change or process, then verb ‘ser’ will usually be used.
Examples
It is a quite complicated topic to understand immediately, so let’s see a first example:
-Marta es vaga
-Marta está vaga
In the first sentence the meaning would be: Marta is lazy whereas the second refers to a feeling happening now: Marta is feeling lazy.
We would first consider that Marta is lazy as part of her character. However with the second example, we assume that Marta is usually not lazy but going through a period of laziness.
The difference between these two verbs can also happen when describing physical appereance:
-Carlos está calvo
-Carlos es calvo
First sentence presents the characteristic as a result of a process; second one describes the subject, just like that, including him in a certain category (bold people).
This main difference explains the fact that some adjectives can only be used with verb ‘ser’ as they are inherent to the subject.
For example:
Celia es de Sevilla – Celia is from Sevilla
Others adjectives will only be used together with verb ‘estar’ as they describe state or condition that always are result of an action or process. For example: La silla está rota (the chair is broken) // Estoy cansado (I’m tired).
Now let’s see some examples of adjectives that can be used both with ‘ser’ and ‘estar’ which will change the meaning of the sentence:
Carlota es lista – Carlota is smart
Carlota está lista – Carlota is ready
El coche es nuevo – The car is new
El coche está nuevo – The car looks new (the car isn’t new but looks like it is)
For conjugation of ‘ser’ and ‘estar’, you can visit this page.