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"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

Logic was the study of the principles of reasoning. As a form of science, logic was used to solve various problems through the application of deductive reasoning. The absence of logic was known as illogic.

Vulcans adopted logic as their way of life, a life of order and control through logic. (ENT: "The Andorian Incident") Surak introduced the principles of logic to his people in the hope of stopping the destructive wars which plagued Vulcan. His hope was that by embracing logic above emotion, the Vulcan people could reign in the savagery of their emotions and create an ordered society. Some basic principles of Vulcan logic were laid out in the First Doctrines of Logic. (DIS: "Light and Shadows")

Although the Vulcan majority lived by logic, there were some who tried to balance their emotions and logic; they were better known as V'tosh ka'tur, Vulcans without logic. (TOS: "The Savage Curtain"; TNG: "Gambit, Part II"; ENT: "Fusion") There were also Vulcans, like Sybok, who rejected logic outright and embraced emotion. (Star Trek V: The Final Frontier)

Other Vulcans chose instead to further develop their mental discipline through the Kolinahr ritual to the point of purging all vestigial emotions and living solely by pure logic. This process could involve years of intense study and meditation. (Star Trek: The Motion Picture; VOY: "Flashback", "Gravity", "Fury")

Several machine-based lifeforms strictly followed logic as well:

See also[]


References to logic[]

"Your illogical approach to chess does have its advantages on occasion, captain."
- Spock, to Kirk

In the final draft script of "Charlie X", Spock instead described Kirk's approach to chess as "eccentric."

"You cannot succeed, commodore. Your only logical alternative is to return to the ship."
- Spock, to Commodore Matt Decker
  • TNG:
    "I saw you crying."
    "I did not cry"
    "I was there, I saw the tears."
    "You exaggerate, captain. I recall only one tear."
    "So you were emotionally affected by the music."
    "That is not possible."
    "You still haven't answered my question, Sarek. Is it logical for a Vulcan to cry?"
    - Picard and Sarek
    '"It is illogical for a Vulcan to show anger! Illogical! Illogical! Illogical! Illogical!"
    - Sarek, raging against Picard's arguments
    "I will not read this or any other statement."
    "If you do not, you will die; all of you will die."
    "Since it is logical to conclude that you will kill us in any event, I choose not to cooperate."
    (enraged) "...I hate Vulcans!"
    - Spock and Sela
  • DS9:
    "We have all suffered losses at the hands of the Alliance. Nonetheless, logic dictates caution in the face of a superior enemy".
    - Tuvok
    "The question of Commander Worf's motive is relevant. I will allow you to explore this issue but only as far as logic permits".
    - T'Lara
  • VOY:
    "One could say that you were both the doubter and the doubted. I do not envy the paradox of logic that you were faced with in that situation."
    - Tuvok

    The concept of "the doubter and the doubted" is present in various Earth philosophies containing a strong meditative component, like Buddhism and American Transcendentalism. The exact phrase may have been borrowed by writer Brannon Braga from Ralph Waldo Emerson's poem, "Brahma".

    "You can use logic to justify almost anything. That's its power, and its flaw."
    - Kathryn Janeway
    "Structure, logic, function, control. A structure cannot stand without a foundation. Logic is the foundation of function. Function is the essence of control. I am in control. I am in control."
    - Tuvok, attempting to build a keethera
    "Your instincts were correct. However, one day your intuition will fail and you will finally understand that logic is primary above all else. Instinct is simply another term for serendipity."
    "And one day, Mister Vulcan, I'll get you to trust your gut."
    - Tuvok and Neelix, debating the value of logic
    "Sing or you will die."
    "Then I'll die."
    "Seven, you are a valued member of this crew. The logical response would be to grant his request."
    "Logic is irrelevant. One day the Borg will assimilate your species despite your arrogance. When that moment arrives, remember me."
    - Seven of Nine, refusing to sing for Turanj, despite Tuvok's plea
    "We're talking about a woman who has alien tendrils sapping the life out of her. She's obviously not thinking straight."
    "On the contrary. Her concerns are based in logic."
    "If The Doctor uses knowledge that Moset gained through his experiments, we would be validating his methods, inviting further unethical research."
    - Tom Paris and Tuvok, arguing over B'Elanna Torres's refusal to allow a holographic program of Crell Moset to treat her
  • DIS:
    "Spock asked the most amazing questions. It's completely logical, yet somehow able to make everyone see that logic was the beginning of the picture and not the end. He was ahead of all of us in that way."
    - Christopher Pike to Michael Burnham regarding Spock
  • Movies
    "Logic clearly dictates that the needs of the many outweigh the needs of the few"
    - Spock
    "Or the one"
    - Kirk
    "Logic is the beginning of all wisdom, not the end."
    - Spock
    "Even logic must give way to physics."
    - Spock, to Valeris
    "Logic offers a serenity Humans seldom experience. The control of feelings, so that they do not control you."
    - Sarek, to Spock
    "You used what he wanted against him. That's a nice move."
    "It is what you would have done."
    "And this, this is what you would have done. it was only logical."
    -James T. Kirk and Spock

It is debatable whether Vulcan usage of the word "logic" is consistent with the real-world concept of logic. This question has never been discussed on-screen or in canon sources.

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