19.4 Das Thema der Ausstellung waren die Höhlenmenschen. Why is waren plural?

Hi sfpugh, 

The subject in the sentence  "Das Thema der Ausstellung waren die Höhlenmenschen."  is actually "die Höhlenmensschen", not "das Thema". The sentence structure here has just changed around. You could also say:

Die Höhlenmenschen waren das Thema der Ausstellung.

It is the same sentence, the sentence units are just ordered in a different way.
Therefore, "waren" is plural because it refers back to "die Höhlenmenschen". 

I hope that makes it clearer to you. 

Liebe Grüße, 
Leah von Rocket German

Thank you
Yes, that makes sense. It is confusing for English speakers because we are so attached to the idea that the noun/pronoun on the left of "to be" is the subject so the verb always agrees with the noun/pronoun on the left if there mismatch in number. (at least I can't think of an example where it doesn't.)

The two sentences I mentioned appeared next to each other which makes it look as though it was intended to teach the difference. This is an example where a short explanation in the lesson would have helped.

Hi sfpugh, 

Thanks for pointing that out. 
I will forward your feedback to our Course Development team. 

Liebe Grüße, 
Leah von Rocket German