Could someone explain why this sentence is in the subjunctive:
"C'est la meilleure chienne que nous ayons eue."
If we have owned many dogs, we would know which was the best, in which case, I thought that the indicative passé composé could be used.
However, if the sentence was saying that "It is the best dog that the word has seen!" ("C'est la meilleure chienne que le monde ait vue !") - that would be a hyperbolic opinion.
Or, am I just not understanding the subjunctive correctly (and that would not surprise me at all :) ).
I think it's probably just that "best" is basically always an opinion--you cannot factually prove a dog is the best--so it's a subjunctive construction. Usually opinions take subjunctive.
There's also just a lot of phrases/etc that always take subjunctive. Here's a detailed explanation of when and in what phrases to use it (past has the same use rules as present): https://www.lawlessfrench.com/grammar/subjunctive/
I did check her page on superlatives that take the subjunctive here:
but she gives this as an example of fact:
C'est le meillieur restaurant que je connais - "This is the best restaurant that I know" as in, I know 10 and, for me, this is the best of them.
I thought the same for speaking of a dog we have had. We may have had 5 but this one, for us, was the best. That is probably why I am confused.
Ohhh okay, huh. Well she says at the top of the page that subjunctive is optional with superlatives, so it's possible that with your scenario it's also optional?
The other possibility is that the fact you are using "nous" form in this case makes it more opinion-y. Like, since you can't be certain that you and everyone else in your family is in agreement about dog quality? Honestly I'm not really sure. And thanks for pointing this out to me!
We can say :
C'est le meilleur chien que je connaisse.
Le meilleur chien, c'est celui que je connais.
in the second sentence the meaning is différent, we are using "c'est celui...", we will never, never, say "Le meilleur chien, c'est celui que je connaisse" never, never...
Oh, c'est difficile même pour les Français.
Oh, it's difficult even for us, French.
En principe on doit utiliser le subjonctif avec les superlatifs pour bien marquer la subjectivité et que c’est un jugement plutôt qu’une indication décrivant la réalité.
In principle one must use the subjunctive with the superlatives to mark the subjectivity and that it is a judgment rather than an indication describing the reality.
Maybe you're confused because the example you're talking about doesn't actually use the subjunctive e. g. "c'est le meilleur restaurant que je connais."
From what I've grasped over the course of my French learning, the subjunctive with superlatives is optional because the subjunctive is supposed to represent certainty/uncertainty in certain situations. The subjunctive is used with the superlative essentially to make it known whether or not you believe you're 80% correct or 99.99% correct. The use of the subjunctive shows a more moderate opinion when compared to a superlative without the subjunctive.
C'est la plus belle maison que je n'aie jamais vue --> This sentence using the subjunctive shows that the speaker believes the house is quite enthralled by the beauty of the house in the moment, yet the house may not truly be the most beautiful one they've seen based on your opinion.
C'est la plus belle maison que je n'ai jamais vue --> This sentence omits the use of the subjunctive because the speaker is absolutely sure that the house they're speaking of is the most beautiful house they have ever seen.
I hope this is helpful :)
I used that example precisely because it was given by the cited website as an example where the subjunctive was not needed.
EDIT: I have only just noticed Pierre's comment that the original poster of this example was, in fact, incorrect and should have used the subjunctive, so it all makes sense now. Thanks anyway :)