Shal'tiar was a temporary state of being among Vulcans. Confronted by a problem which seemingly cannot be solved through logic, a Vulcan may enter the state of Shal'tiar, where he or she abandons logic and begins to attempt to solve the problem by any means necessary, even against logic and ethics. During this time the Vulcan in question becomes obsessive and sometimes even dangerous. (NF novel: Treason)