"Il y a un chat et une souris."
Translation:There is a cat and a mouse.
Ya, I can see where you might think that.. Il y a is a set phrase, there is, there are.. one of the few things I did still remember from high school French.. Learning a new language is a process, to be sure.. on a positive note, it is said learning a new language helps to stave off dementia, as it activates different parts of our brains, possibly that have not seen activity in a long time!! Bonus..
As Shirlgirl wrote, think of "il y a" as a phrase, not as individual words. It simply means "there is/are." ... I am presently taking a course for Literacy Tutors, and am being reminded of all of the odd phrases we have in the English language. Think of the phrase, "on the house." The word "on" has nothing to do with my getting a meal for free! Do I have to climb up to the roof to locate the meal? Or, what in the world does "open up to me" mean? One certainly cannot deduce the actual meaning from thinking of the individual words! I'm going to keep my eye on you! LOL
I thought cat was la chatte; didn't I see that in an early animals lesson?