They are both correct in that they are the third person conjugation of Ser and Estar. The difference however is that the use of es/ser suggests that the subject is always or inherently kind. The use of está/estar suggests that the subject is only kind on this occasion. It can be also explained with the example "The apple is green". If it is a green variety and therefore always green then you would use es/ser. If it was green from being unripe then you would use está/estar.
when do we use es & when do we use esta like es muy amable why not esta with accent on top of a?
December 7, 2010