Would you use ser for permanent conditions?
I know that to say someone is sick you would use estar, but what if that person is always sick, like if they are diabetic or if they have cancer? Would you still use estar to say "he is sick" if the condition was permanent?
3 Answers
That is why the permanent/temporary criteria is usually not recommended. it requires a definition of what time limit is temporary and what is considered permanent. And then there are the contradictions like "está muerto". The CID reasoning is more practical.
Ser is used for personality or inherent qualities. Using Ser with enfermo would more likely define the attribute that the person was sickly (not robust and healthy, but slight, weak and prone to disease) or depraved (a mental condition).
The fact that he had a chronic, or incurable disease would still imply the use of Estar unless it was being used as a classification: he is a person with cancer, he is a diabetic. In that context, permanent or temporary is irrelevant, you are just identifying the person as belonging to a separate group possessing that attribute. Notice that you would use Ser with the noun: Es [un] diabético.
¡Hola!
Ok, when you are sick, we say "tu estás enfermo" (verbo estar), however, if you want to say that you've got cancer, we say "tu tienes cáncer". If you're always sick, we say "Tu siempre estás enfermo". Although the condition is permanent we still use the verb "estar", if it's permanent, we only add "siempre" (always).
Note: In all the examples, the word "tú" could be eliminated.
Hope I've helped you 
Here is a joke: Patient: Doctor, doctor soy asmático. Doctor: Es grave, Patient: No es esdrújula.
