Learn French: Quand bien même vous auriez ce pouvoir, vous seriez vulnérable. - Even if you had this power, you would be vulnerable.

Unlike the word si (if), which pairs with the imperfect tense to express a hypothesis (si vous aviez), the phrase quand bien même always takes the conditional mood. So, even though English uses a past tense ('had'), French strictly requires the conditional (auriez) after this specific expression.

How is this different from using même si?

The meaning is very similar, but quand bien même is a bit more formal or literary than the everyday même si. The biggest difference is grammatical: même si is followed by the imperfect tense (même si vous aviez ce pouvoir), whereas quand bien même requires the conditional (quand bien même vous auriez ce pouvoir).

Since the subject is vous, why doesn't vulnérable have an 's' at the end?

The lack of an 's' reveals that vous is being used as the formal singular here, meaning the speaker is addressing only one person respectfully. If they were addressing a group of people, it would be spelled vulnérables.

Is the 'd' in quand pronounced in this sentence?

No. The 'd' in quand is usually only pronounced (as a 't' sound) when making a liaison with a following vowel. Since the next word (bien) starts with a consonant, the 'd' remains completely silent.