Only if they're deliberately introduced. Very little accidental ambiguity makes it into legal contracts (unlike legislation and agency regulation!), but deliberate ambiguity is a very valid strategy, and often is designed to break the spirit of an agreement by creating loopholes in the letter. Always, always, always assume that if the same language could be interpreted two different ways, the guy on the other side of the table intends to argue the one that hurts you the most.