Board Thread:Lore Discussion/@comment-85.74.137.231-20130605091958/@comment-13199219-20130725044518

People keep saying that in order to use the dragon shout, a dragonborn must have absorbed a dragon soul first. That is just a game mechanic. The Greybeards, and Ulfric Stormcloak learned how to shout before the dragons returned.

In a nutshell it looks like this: people with dragonblood are of the line of a dragonborn (The Septim line post Talos), or have been chosen by Akatosh (Like Alessia); People who are dragonborn have dragonblood and also have the soul of a dragon and thus can absorb souls. Both types have been chosen by Akatosh. One (Dragonblood) can be passed on. The other (Dragonborn) is a direct gift and cannot be passed on or inheirted. One could look at dragonblood as being a 'perk' of being dragonborn; the ability to pass on the blood to descendants. Of the two, only dragonborns learn shouts easily.

The greybeards specify that the Dragonborn must be 'Dragonborn' because he can learn the shouts so easily, whereas for them it takes years of meditation and practice. This long period of practice is implied to be needed for all who are not Dragonborn (Such as Ulfric Stormcloak, who will use Unrelenting Force as an attack when attacking in the Palace of the Kings).