"Why is he so serious?"

Translation: Dlaczego on jest taki poważny?

[HelbentForleder]

Okay... I don't get it. Could someone someone explain how 'On jedt taki poważny' s the same as 'tak poważny'? I always thought 'taki' only meant 'that kind of'. As an example, ' On jest taki po prostu.' in others words, 'He's just lke that'.

[mihxal]

"Tak" can be compared to English "so" (adverb). "Taki" is similar to "such" Is there much difference between them in English? In Polish not so much.

[Ten_Pies_I_Brew]

Well, you can't say "He is such serious" in English. You can say "He is such a serious person", though... My first guess is that "so" is for adjectives (like "serious") and "such" is for noun phrases (like "a serious person").

[RobinTrndr]

'Dlaczego on jest tak serio?' isn't correct?

[Jellei]

"serio" is an adverb, and on top of that it's a colloquial one.

"On tak (na) serio?" would work as "Is he for real?", "Is he serious?" in a colloquial way. Like when you hear a guy saying that stones have feelings and you wonder if he is joking or speaking seriously.

[dlhgl]

Are "tak" and "taki" always interchangable or are there sentences where only one of them is correct?

[Jellei]

For sure you cannot substitute "tak" + adverb with "taki", that wouldn't make sense.

For adjectives... I think you can always change "taki" to "tak", although there may be something that I can't think of right now.