ESTAR (to be) and HAY (there is/there are) both can be used to indicate the presence of something or someone. Though, they are rarely interchangeable.
Hay flores (there are some flowers).
Las flores están en el jarrón (the flowers are in the vase).
1. Hay, the impersonal form of “haber” in the present tense, is used to indicate the mere existence of the person or thing. While estar, on the other hand, is used to say where something or someone is located.
Sometimes, the difference in meaning between estar and haber can seem subtle.
El loro está en la jaula (the parrot is the cage).
Hay un loro en la jaula (there is a parrot in the cage).
2. As a practical matter, there’s not actually a lot of difference in meaning, but estar is mainly used when a specific person or thing is referred to (I know about what parrot I am talking about), but hay is used more generically (it can be any parrot, I don´t know or it is not relevant).
Hay una mujer en el jardín (there is a man in the garden).
Hay alguien en el jardín (there is someone in the garden).
3. Whereas, a noun preceded by a definite article (the word el, la, los or las, meaning “the“), a demonstrative adjective (a word such as ese or esta, meaning “that” or “this,” respectively) or a possessive adjective (such as mi or tu, meaning “my” or “your,” respectively) normally would be used with estar.
El cartero está en el jardín (the postman is in the garden).
Mi mujer está en el jardín (my daughter is in the garden).
4. With nouns that can’t have a location, haber must be used:
No hay problema (There is no problem).
Hay riesgo inmediato (There’s an immediate risk).
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