Learn Portuguese (Portugal): Esta é a propriedade luminosa, sobre a qual nós falámos ontem. - This is the bright property, about which we spoke yesterday.

In Portuguese, when you use a preposition with more than one syllable (like the two-syllable sobre), you must follow it with o qual, a qual, os quais, or as quais rather than the simple relative pronoun que. Since the noun we are referring back to (propriedade) is feminine and singular, we use a qual.

Could I express "about which" using a shorter preposition in this sentence?

Yes! The verb falar can be followed by sobre (about) or de (of/about). If you used de, which is only one syllable, you would use the simpler que instead: Esta é a propriedade luminosa, de que nós falámos ontem.

Why does falámos have an accent mark on the second "a"?

In European Portuguese, this accent mark is crucial because it tells us the verb is in the past tense. The accented nós falámos means "we spoke", whereas the unaccented nós falamos means "we speak" in the present tense.

Is esta related to the word propriedade even though they are separated in the sentence?

Yes. Esta means "this" (feminine singular) and acts as a demonstrative pronoun here. It must match the gender and number of the noun it introduces, which is the feminine singular a propriedade.