Logic

Logic is the principle of reasoned thinking.

The Vulcan people adopted logic as a way of life and deeming emotions illogical suppressed theirs. The Vulcans of the lost colony of the Last-of-all-Cities left Vulcan before the spread of logic amongst their people and when they were rediscovered were disgusted by what had become of their people. They planned to hijack the the USS Enterprise and return to Vulcan as conquers. Spock could not understand this noting how illogical their violence was given they had the capacity to construct an impulse engine themselves. (EV comic: Cloak and Dagger)