Cognates are a pair of Telepaths who work together and have a special, and rare mental connection. They can achieve things that a single Telepath cannot by combining their energy and balancing each other's personality. Cognates are required to share everything with each other and their bond is based on trust. It was noted by Tiergan in Book 8, however, that the Cognatedom shared by Sophie and Fitz might still be possible even if some secrets are kept from each other, an approach that requires maturity and trusting the other no matter what. Tiergan, as well as countless others, believed that this was the highest level of Cognatedom. Accepting the other person's limitations (of what they can share) can even enhance the bond between Cognates that reach this level. A Cognate must also have a special connection with the other.
The special bond between Cognates is strong but can be broken if the trust between the two is breached. It is very rare for a Telepath to find their desired match, much less achieve Cognatedom because they have to be so open and perfect for each other. It can be very hard to share everything with another person, shown by Sophie in Neverseen, Lodestar, and Nightfall when she hides her crush from Fitz.
Tiergan and Mr. Forkle tested whether Sophie and Fitz could become cognates by seeing whether Sophie could teach Fitz an impossible telepathic skill, which she succeeded in. They began their training in Neverseen and have maintained a healthy connection throughout. In Legacy, they go through a bumpy patch in their cognatedom, but afterwards, they resume working on their bond. Fitz often uses the fact that they are cognates as a reason to work with Sophie.
- Mr. Forkle and Mr. Forkle (deceased)
Mr. Forkle and Mr. Forkle shared every memory and secret with each other even before they manifested as Telepaths — when one twin was dying shortly after the events of the Peace Summit at Lumenaria, he used his final moments to share all his memories with the other twin so that there would be "no gaps" in his, or rather, their memories. The Only thing the late Mr. Forkle did not share was the pain in his final moments.