"He is a man."
Translation:On jest mężczyzną.
I wrote "on jest mężczyzna" and it gave it as correct, although this is indicative and it should be instrumental (as here above). Is indicative also correct in this case, and if so why?
Most people don't have the Polish keyboard, so they can't type the ą. It would accept it if you'll write 'on jest mezczyzna', which is completely incorrect.
That said, since it does make a big difference in Polish, you can use the onscreen buttons in the web interface, and lots of mobile keyboards allow accented characters. That doesn't really suffice for the timed tests, but your operating system may have a Polish mode available for English keyboards (certainly my Windows 8 version does).
What does instrumental mean? I understand that it has a -ą at the end of it.
Well, as you probably know, Polish has 7 cases, which depend on the function in the sentence, the fact that certain verbs or prepositions need certain cases, etc. Without understanding them, you will not be able to learn Polish.
Now, Instrumental is a case that has three main meanings: one, that you use X as an Instrument; two, that you are doing sth "with X"; and three, in defining. At the beginning of the course, we focus on the third meaning.
First, I'd recommend taking a look here: https://www.duolingo.com/comment/16373167 - especially Parts 1 and 2.
Secondly, you can search for topics about cases in this post: https://www.duolingo.com/comment/16296174
And of course there's always this website: http://mowicpopolsku.com/polish-grammar/cases/instrumental/
As for the -ą ending, it is true for nouns that end with -a in their basic, Nominative form. These are almost all feminine nouns and a few masculine ones. As "mężczyzna" means "a man", it is one of those masculine examples.
"Mężczyzną," with a nasal "ą." That's the instrumental case form of "mężczyzna." Polish uses the instrumental case after verbs describing being or becoming.
Does Polish not allow the omission of the verb to be? I only ask because it's possible in pther languages.