Breakdown of Дискуссия была долгой, зато его аргумент убедительный.
быть
to be
долгий
long (of time)
его
his / its (possessive)
зато
but on the other hand
Questions & Answers about Дискуссия была долгой, зато его аргумент убедительный.
What exactly does зато mean here, and how is it different from но?
Зато translates to "but on the other hand" or "but at least." While но (but) just shows a simple contrast, зато is specifically used for compensation—when a negative or less desirable point (the discussion being long) is balanced out by a positive reward (the argument is convincing).
Why is долгой in the instrumental case instead of the nominative?
In Russian, adjectives that follow the past tense of the verb "to be" (была, был, etc.) are often put in the instrumental case (долгой) rather than the nominative (долгая). This is especially common to describe a temporary state or a characteristic that was true during that specific past event.
Why is there no verb in the second part of the sentence (его аргумент убедительный)?
The second clause shifts to the present tense ("his argument is convincing"), so it uses the standard Russian "zero copula" (dropping the present-tense verb "to be"). Even though the discussion was in the past, the speaker is stating that the argument itself is still fundamentally convincing right now.
Could we use the short-form adjective here and say его аргумент убедителен?
Yes, absolutely! At the B1 level, you will often start seeing short-form adjectives used for abstract qualities or statements of fact. Saying его аргумент убедителен sounds very natural and slightly more formal or emphatic than the full-form убедительный used here.