I will seek truth
Truthwatcher oaths are themed around seeking to find ultimate truth and sharing it. They are very concerned with knowledge and the proper exploitation of it. Note that this should not be confused with the Lightweavers, whose oaths are themed toward personal truths about themselves, said for reasons of self-actualization. Truthwatchers are more concerned with the fundamental truths of the universe, and whether or not those in power are being truthful with the people they lead.
The Truthwatchers are seen as quiet, largely known as the most scholarly Order of Knights Radiant. They tend to attract scientists primarily, but also scholars or thinkers of all types. This extends to some who might not normally be known as scholarly but instead as someone often consumed by their own thoughts. In general, they tend to be reserved, particularly in person, though a small minority of Truthwatchers are greatly concerned with the actions of the powerful and might be likened to investigative reporters. These make their opinions known loudly and forcefully, particularly if they think someone in power is abusing that power or lying about fundamental truths. Note that, as with all Knights Radiant, there is great disagreement within the Order about what is the truth. However, Truthwatchers tend to approach these discussions with enthusiasm, even if they generally prefer to write their opinions rather than speak them. Among the Knights Radiant, the Truthwatchers tend to be those who hold the knowledge and secrets of Surgebinding and are the ones to discover many of the newer advances in things like fabrial technology.