Ser vs estar again (sigh)

Question

Hi, Shui, is there a difference between “este está compuesto por” and “este es compuesto por”? I would have expected the ser form in this context. From reverso.com I see both forms are quite common. Why would you choose the estar form in this case, and would the ser form be wrong? Thanks!

Answer

Hola Gromit
The passive can be formed with the verb ser or the verb estar. We use the passive with ser when we talk about actions that indicate and put the emphasis on the actual process of doing something; for example:

El ladron es arrestado por la policía.
The thief is arrested by the police.

We talk about the process of being arrested here.
However if we say:

El ladrón está arrestado.
The thief is arrested.

Here we refer to the end result. So, as a result of being arrested he is [now]arrested.
With estar we show the result (not the process).
In the example you see in the video, using está compuesto, we are expresing the result too. 
We hardly ever see this verb being used with ser, we generally use it with estar.
Here's a lesson that will help:
Pasiva with estar 
Saludos
Inma