I have been questioning this for a while. I am roleplaying with my theif character, and he is not a dragonborn, he won't be doing the MQ. However he is able to study the Thu'm and understand words through study. I see Jarl Ulfric and the Greybeards know the shouts, but how does one learn a shout yet not have to absorb the soul of a dragom?

The only way for me to learn a new shout is to defeat a dragon then absorb the soul. Forcing me to become the Dragonborn. Does Ulfric or the Greybeards do this? Are they secretly Dragonborn?

Things that make you go... hmmm This is indeed a very good question, considering that the dragons have only come back recently.

So, since there were no dragons in Skyrim, how would Ulfric learn his shout? How old are the Greybeards? Did they learn it during the Dragon Wars? Where they present at that time? Did Paarthurnax teach them through some kind of magic? How did the three Nord Heros you meet in Sovngard learn to shout? Did they absorb souls? Or is the soul absorbing thing new, since you permanent kill the dragon with it? Would it otherwise come back to life over and over?

Lots of questions...

http://www.imperial-library.info/content/dragon-war It says here that some dragons sided with men and that from these dragons men learned magics to use against dragons. Maybe shouts can be taught without using souls?

Note that you don't have to get a dragon soul to learn a shout. It's enough when you are "given one's understanding of a thu'um". You learn all the Unrelenting Force shouts this way, at least, and a couple of others.

As far as I know, nothing states that Ulfric could not be a Dragonborn. I bet he has only learned those shouts when he was training with Greybeards. That he has trained with those is mentioned in the game.

Greybeards are ancient. Can't bother to find out more about their origins now. Use the net. Imperial Library and UESPWiki are your friends. Obviously they have learned from the dragons, at least from Paarthurnax.

Arngeir tells you that it takes a normal person years of study to master a thu'um.

Ulfric had a wife that nagged to much, so he kept shouting at her. He learned the Thu'um that way

The Thu'um is an ability that any Nord can learn and master...with practice. It takes decades of training to master the Thu'um. This is how the Greybeards, Ulfric, the Draugr, and the Heroes of Sovngarde learned to use the Thu'um. What makes the Dovahkiin so special, is that he/she was born with the soul of a Dragon, therefore, the Dovahkiin can not only be a different race than Nord and learn the Thu'um, but can also absorb the souls of Dragons in order to gain their understanding of the Thu'um, basically taking a shortcut to mastery of the Thu'um without the actual decades of practice.

This brings up a few questions though. Since Bethesda has established the Thu'um as a gameplay mechanic in TES V: Skyrim, will the Thu'um continue to exist in later installments to TES series, as a Nord racial? Maybe the Nord racial "Battlecry" is a lesser version of the "Dismay" Dragon Shout.
Another question is, since Alduin can resurrect dead dragons with the "Slen Tiid Vo" shout, can that same shout also resurrect a dead Dovahkiin, since they have the soul of a dragon? It'd be a pretty interesting plot twist if that shout could be used to resurrect Tiber Septim (Talos), and he proceeds to unify Tamriel once again and wipe out the Thalmor. On the topic of the "Slen Tiid Vo" shout, i can see someone creating a mod that allows the PC to learn it (Possibly upon the death of Alduin), and it acts like an AoE Reanimate on anything in it's path, similar to the Ritual Stone. Doing so may even consume Dragon Souls to reanimate powerful creatures, giving a use to Dragon Souls once you've maxed out all the other Dragon Shouts.

Al Bundy...Master of the voice...