אל לנו להישאר פה.

English Translation

We must not stay here.

In this case because it is אל לנו it means we must not. But if it is spelled with an ע as in על לנו להישאר then it is we have to stay (it is upon us to stay)? Is this correct? Is there a way to distinguish between these two opposite meanings when listening if you don’t have the spelling?