‘I am the Mouth of Sauron’

In The Black Gate Opens, the Mouth of Sauron hails the Captains of the West with an introduction: 'I am the Mouth of Sauron'. This is somewhat problematic, because earlier in The Lord of the Rings, Aragorn says of Sauron that 'Neither does he use his right name, nor permit it to be spelt or spoken...' (The Two Towers III 1, The Departure of Boromir). The Mouth of Sauron, though, uses the name several times without apparent embarrassment.

All the evidence suggests that Aragorn is simply wrong. Not only does the Mouth of Sauron use his Lord's 'right name' freely, but so does the messenger sent to Dáin in Erebor. Indeed, we hear about Dáin's messenger at the Council of Elrond, at which Aragorn was present: he must have been - to use Gandalf's word - 'inattentive' on this point.

One possible reason for Aragorn's error is that his information is out of date. For most of the Third Age, Sauron had been building his strength, in secret, at Dol Guldur. Given his need to remain hidden, it's natural that he would ban his servants from using his real name. Any detailed information that Aragorn had about him and his ways would date back to Gandalf's spying expeditions in this period.

The Tale of Years entry for the year III 2951 states 'Sauron declares himself openly...' At this point, about seventy years before the War of the Ring, Sauron no longer felt any need for secrecy, and so presumably permitted his name to be used from that point on. Aragorn, of course, would have had no way of knowing about this change, which would explain his mistake.

Did Tolkien intend all this? Probably not - it seems much more likely that Aragorn's words were a casual slip of the author's pen. The explanation given here, though, does make a certain amount of sense within the context of the story.