Related:

• Worry is a human emotion. -- Spock, "Journey to Babel," stardate 3842.4
• Humans smile with so little provocation. -- Spock, "Journey to Babel," stardate 3842.3.
• Vulcans do not approve of violence. -- Spock, "Journey to Babel," stardate 3842.4.
• Threats are illogical, and payment is often expensive -- Sarek of Vulcan, "Journey to Babel", stardate 3842.
  3...
• Spock: "I've never seen him look so happy." -- "Journey To Babel", Stardate 3842.3.
• It would be illogical to assume that all conditions remain stable.
  -- Spock, "The Enterprise" Incident," stardate 5027.3...
• It [being a Vulcan] means to adopt a philosophy, a way of life which is logical and beneficial.
  We cannot disregard that philosophy merely for personal gain, no matter how important that gain might be....
• Amanda: "Oh, that's not a dirty word!" -- "Journey To Babel", Stardate 3842.3.
• Andorian Ambassador: "Devote yourself to motivations of passion.
  -- "Journey To Babel", Stardate 3842.3....