Why subjunctive in this sentence

[Aprendo]

"La felicidad no es un valor que pueda ser medido con precisión, discutido en plebiscitos ni analizado por especialistas."


I don't know why the subjunctive "pueda" is necessary here.

The speaker is giving an opinion in the negative (no es un valor). This is the reason?


Thanks again in advance.

This passage is from "Adulterio" by Paulo Coelho, p. 34.

[Rusty]

Since this is an opinion, the mood is subjunctive. It doesn't matter that it's negative. If this weren't an opinion, the indicative mood would be used instead.

[Aprendo]

^ Gracias, Rusty.

[AngelicaDeAlquezar]

I agree with Rusty.
Also, the structure "no + ser + que" takes the subjunctive in this kind of context.

-No es que quiera asustarte, pero hay un fantasma en la casa.
It's not that I want to scare you, but there's a ghost in the house.
-No me cae bien Pedro. No es que sea antipático, pero tiene algo desagradable.
I don't like Pedro. It's not that he's unfriendly, but there's something unpleasant about him.
-No es que me encante la idea de salir de viaje, pero lo haré por ti.
I'm not especially happy with going on a trip, but I'll do it for you.
-No era que me gustara estar a dieta, pero mi madre no me dejaba comer dulces.
It was not that I liked being on a diet, but my mother wouldn't let me eat candy.
-No le voy a decir nada, pero no será que me lo agradezca.
I'm not going to tell him anything, but he will certainly not be thankful for that.