Ser, Estar Before Adjectives: "Permanent" and "Temporary?"  

It is often said that ser is used before an adjective when a "permanent" quality is being described, and that estar is used when the quality is "temporary."

While this can account for many cases, it can also be misleading. The terms inherent (ser) and non-inherent (estar) are preferible.

For example, one uses ser to say that someone is young (Luisa es joven), if the meaning is that the person in question is a young person. The speaker is expressing the perception that this is what she is by nature, or inherently. Youth is, of course, not permanent. Luisa está joven would mean that Luisa (who might not be that young in years) is looking youthful right now, perhaps because she's been taking good care of herself.

On the other hand, estar is used to say that someone is alive or dead and of course only the first of these is "temporary." Since all human beings are first alive, then dead, neither state is perceived by Spanish speakers to be an inherent (definitive) state, hence the use of estar (El padre de Julio está muerto, pero su madre está viva).

Hence too the inadequacy of temporary/permanent to describe this aspect of the ser/estar distinction.