On OrthodoxWiki it says that the filioque violates the Canons of the Council of Ephesus, because it's an addition to the Nicene Creed.
The Catholic Encyclopedia says "[But] that creed itself would be abolished by this decree if it is taken too literally." But does not elaborate much on this. If the problem is taking the canons "too literally" then how should the canons be read?
How do Catholics explain that the filioque does not violate Ephesus?