Vulcanism is the belief that we can only trust our reason and that emotions are not effective arbiters of truth. That is not to say that emotions don’t have value — they can enhance the quality of life and also inspire hypotheses about the world and its organization. However, the last word on any question of veracity must always be rendered from a rational, scientific approach.
Vulcanism was created for the Star Trek literary universe by Gene Rodenberry, although various other authors have contributed to its mythology, notably Diane Duane. According to the mythos, inhabitants of the planet Vulcan had been an impulsive and violent people who worshipped many different gods until a sage named Surak taught them the value of rationality and they discovered its power as a peacemaker. Rather than discard their old religions, Vulcans kept the practices and rituals that still made sense employed the ecclesiastical structure to help protect and promote these new rational ideas. Within its literary universe Vulcans have discovered scientific proof of the soul, which informs their thinking on many levels. Human Vulcanists outside of the Star Trek universe still have no proof to go on, so belief in the soul would contravene their own logical Vulcanism. However, they may choose to entertain the notion as a mythological metaphor.
To keep their logical minds sharp, Vulcanists study logicology (the study of logical fallacies) and biasology (the study of cognitive biases), along with other elements of rationalism. Various forms of meditation are also followed to the extent that they seek rational understanding rather than a quest for mystical or magical goals. Within the Star Trek universe Vulcans are expected to undergo a ritual called “kahs-wan” which involves surviving ten days without food, water or weapons in a dangerous place Vulcan’s Forge. Outside of Star Trek, Vulcanists may undergo trials of strength or will, but nothing with potentially injurious or fatal consequences.
Challenge your preconceptions, or they will challenge you.
— Star Trek: Enterprise, Season 1 Episode 4, “Strange New World”
Logic is the cement of our civilization, with which we ascend from chaos, using reason as our guide.
— T’Plana-Hath, Matron of Vulcan Philosophy, Star Trek IV: The Voyage Home
After a time, you may find that having is not so pleasing a thing after all as wanting. It is not logical, but it is often true.
— Spock, Star Trek: The Original Series, “Amok Time”