Learn German: Ich hoffe, dass du morgen Zeit hast. - I hope that you have time tomorrow.

The word dass (that) is a subordinating conjunction. It creates a dependent clause and forces the conjugated verb (in this case, hast) to the very end of the sentence.

Is the comma before dass mandatory?

Yes! Unlike in English, where a comma before "that" is usually wrong, German strictly requires a comma to separate the main clause (Ich hoffe) from the subordinate clause (dass du morgen Zeit hast).

What is the difference between dass and das?

They sound exactly the same, but they have different jobs. The word dass (with a double 's') is a conjunction that connects two clauses, translating to "that". The word das (with one 's') is either the neuter article "the" (like das Haus) or a demonstrative pronoun (like Das ist schön meaning That is nice).

In English, we often drop the word "that" and just say "I hope you have time tomorrow." Can I drop dass in German?

Yes, you can! However, if you drop dass, the second part becomes a normal main clause and the verb moves back to its normal spot in the second position: Ich hoffe, du hast morgen Zeit.