I am somewhat confused by the use of singular langauge to discuss generally true statements, for example:

> 
> A cat is smarter than a dog.
> 
> 
> 

The intention of this statement is to say that in general any given cat will be smarter than any given dog.

However, my interpretation of this is that it simply states there is a cat that is smarter than a dog, a statement which is different and much harder to prove.

Why is it that the first interpretation is meant when a statement like this is used?