czy is a question word for yes/no questions. It can be always used with yes/no question. It is used with longer questions, when you want to stress the question word, and in formal writing. It is also used when intonation can be not heard. I would encourage learners to use it all the time, as their intonation may be unclear.
Can somebody enlighten me on when to pronounce "dz" as a "light" affricate (/d͡z/, voiced alveolar affricate) and when a hard one (/d͡ʒ/, voiced postalveolar affricate)? I have noticed that on Duolingo, Widzę is pronounced with an alveolar affricate while Widzisz has the postalveolar one. Pronunciations on Google translate are consistent with those on Duolingo, whereas both are pronounced with /d͡ʒ/ in the samples on Forvo.
To add to the perplexity, the Wiki article on Polish phonology seems to imply that "dz" is always pronounced /d͡z/ (which is certainly not the case with Widzisz). I also see that the article doesn't list any postalveolar affricate at all. This makes me hypothesize that /d͡z/ and /d͡ʒ/ are allophones in Polish, maybe even with complementary distribution (like, for example, /d͡z/ before "e" and /d͡ʒ/ before "i").
It would be great if some native speaker could chime in and help me understand if there is some pattern regarding when "dz" is /d͡z/ and when /d͡ʒ/.
Thank you for the swift reply, Jellei.
Fortunately, I find the pronunciation of "dź/dzi" (technically, /d͡ʑ/ or voiced alveolopalatal affricate) on both Duolingo and other sources to be consistent with the orthography and distinct enough from the two I mentioned before, to avoid any confusion. But the problem of when "dz" is /d͡z/ (as in Widzę) and when it is /d͡ʒ/ (as in Widzisz) persists.
Perhaps it will be a while before I get used to the pattern. After all, I have just started the course. The phonology of Polish, and especially the abundance of fricatives and affricates is really making me love this language. :)
A voiced alveolo-palatal affricate is /ʥ/, not /d͡ʒ/, which is a different sound. Standard Polish has /ʥ/; it does not have /d͡ʒ/ (although this sound may appear in some dialects.)
When dz is followed by i in the same syllable, as in widzisz, it is palatalized and pronounced as /ʥ/ just like dź.