German: Konjunktiv I and II. Most people first learning German will hear the Konjunktiv II in its usage similar to a subjunctive in english ("Wenn das so wäre" - "If it were that way"), but it does so much more. You can switch full sentences to the Konjunktiv II, but that immediately implies that you doubt the statement being presented. For instance, if you say "er hätte es vergessen", you're essentially saying "he allegedly forgot it, but I really doubt it", just by using the Konjunktiv II.

Then, there's the Konjunktiv I, which is similar, but instead of voicing your disapproval, you're staying completely neutral. Taking the example from before, it would be "er habe es vergessen", with which you're saying, "he allegedly forgot it, and I neither support nor disavow that statement" - again, all only with a change of verb form. It's wonderful when you're relaying something someone else said without adding your own evaluation.