"A duck is an animal."

Translation: Kaczka jest zwierzęciem.

[Sweetblue001]

How do you know when to use Ciem and when to use em...sorry just a bit confused on this

[Hania0902]

Me too!! Super confused about this...

[Gom8z]

My rule is 'to' means use the short version and 'jest' the longer

[Jellei]

Well... it looks like a good rule, although sometimes the length will be the same, e.g. with (most? all?) feminine nouns.

[2oocc]

When to decide to use "to" or "jest"

[Jellei]

In a lot of cases, they're completely interchangeable. Have a look here: https://www.duolingo.com/comment/16373167

[AkaRock]

But why is "zwierzem" is not right? animal is also "zwierz"

[MarioZahariev]

Yea, exactly.What't the difference betweeen zwierze and zwierzeciem?

[arthur0703]

Zwierz takes irregular form in the Instrumental case - you should add -ęc-

[Pam201883]

The option to choose "to" is not available in this sample.

[Jellei]

If "Kaczka jest zwierzęciem" was available, and I guess it was, then everything is fine. Well, could be better (see here: https://forum.duolingo.com/comment/27952965), but it's fine.

[samrooney]

I understand kacza to zwierze being right but how is "kaczka jest zwierzeciem" also right? Isn't that 'a duck is animals'?

[tadjanow]

'zwierzęciem' is singular instrumental case

[GraceandRu1]

The explanation Tadjanow and MariZahariev gave is interesting, but I don't find it very helpful. Why do we use the instrumental case when we categorize things?

[Jellei]

Often there's no better answer than "we just do". At least unless someone is educated in the history of language...

[BabaLingva1]

This one is hard to explain in English, since it has no idea of nouns declination/cases.
Try to think of the question not like "what the cat IS" - an animal, but "what the cat is being" (or even "being of") - then it makes more sense to not use just a simple nominative case (an animal), but instrumental.

[ValerieMichonski]

we say the same thing in physics lol

[KristineKr465965]

I said kaczka jest zwierzę. Why is that wrong? Why is zwierzęciem now the only accepted answer?? I'm sure we used that sentence form for "zwierzę" a short while back!

[alik1989]

Kaczka to zwierzę (to + nominative).

Kaczka jest zwierzęciem (jest + instrumental).

https://forum.duolingo.com/comment/16373167