"Do you not see the cat?"
Translation:Ty tu kočku nevidíš?
I said, "Nevidíš kočku?" Why is the word "tu" needed here? I though I was supposed to translate "tu" as "that", so when I saw "the" in English, and not "that" I thought I was to leave out the article entirely.
Not really. It is one certain cat we are talking here about. The cat. To express that somehow in Czech we often (though not always) borrow a pronoun = that. Kočku nevidíš is referring to a cat, do you see any cat out there? But once THE gets in the game we go for TU KOČKU NEVIDÍŠ?