Tradução - Português europeu-Grego - só sei que nada sei...

Mόνο ξέρω ότι δεν ξέρω τίποτα.

You are right Pirulito, this is the perfect syntax, as you say. But I translated it like that for emphasis. The phrase of the anscient greek philosopher Socrates is actually translated in modern greek like that :Ένα ξέρω ότι τίποτα δε ξέρω. However it could have been translated as you said. The only reason i am not changing it is for emphasis.

CC: pirulito