Questions & Answers about To jest chyba nasz autobus.
Why is autobus in the basic nominative case here? Doesn't the verb być (to be) take the instrumental case?
The verb być usually requires the instrumental case when you are defining what someone or something is (for example, On jest kierowcą - He is a driver). However, there is a special rule: when you use the pronoun to (meaning this/that) as the subject, the noun that follows stays in the basic nominative case.
Can I leave out the word jest here, like we often do in simple sentences like To mój brat?
Yes, you can! To chyba nasz autobus is completely correct and sounds very natural in everyday spoken Polish. Including jest just adds a tiny bit of structure or emphasis to the sentence.