In French, you can’t say “I have two” if someone asks you how many cars you own. That would be grammatically incorrect. You have to say “I have two of them.” Your listener must always know what you are referring to, even though it will usually be obvious from the question they asked. There is a whole class of pronouns that exist in French solely for this purpose, while English may have substitutes or no equivalents at all. The thing being referred to by the pronoun is called the antecedent (‘ante‘ meaning ‘before’, as in the word antenatal), or referent.

Quand on y croit – When you believe

This is the French translation of the Prince of Egypt song title. In English, believe stands on its own without an object (though one can infer that it is implied, as in we usually believe in something or someone). In French however, the object or antecedent must always be referenced. Hence the pronoun y, which replaces an inanimate object preceded by the preposition à in a verbal phrase (in this example, our phrase is ‘croire à quelque chose‘ or ‘to believe in something’). ‘Quand on croit’ would be grammatically incorrect because there is no pronoun marking the antecedent.

Il en reste deux – There are two (of it) left

In French, we must say “there are two left of it” or “there are two of it left”. In English, we say “There are two left” leaving our very intelligent listener to fill in the obvious gaps. If you ask me “How many cartons of milk are in the fridge?” and I respond, “There are two”, it is quite obvious I am referring to the milk cartons.