Board Thread:General Discussion/@comment-24991718-20140726213036/@comment-24873188-20150907012024

Arngeir can talk because he is the only one to master the voice so well, he can still speak and control his speech. He is also lv. 150, the highest leveled NPC in the game, right next to Miraak. Ulfric even mentions that Arngeir is the strongest out of all the greybeards in some of his dialogue, before you visit High Hrothgar. He should know because he was with them for 10 years.