Mr. Spock: You're the captain of this ship. You haven't the right to be vulnerable in the eyes of the crew. You can't afford the luxury of being anything less than perfect. If you do, they lose faith and you lose command.
Spock: If I seem insensitive to what you're going through, Captain, understand - it's the way I am.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: Jim, you can't risk your life on a theory!
Mr. Spock: Being split in two halves is no theory with me, Doctor. I have a human half, you see, as well as an alien half, submerged, constantly at war with each other. Personal experience, Doctor. I survive it because my intelligence wins out over both, makes them live together.
Mr. Spock: Your intelligence would enable you to survive, as well.
Captain James T. Kirk: What's the matter with me?
Mr. Spock: Judging from my observations, Captain, you're rapidly losing the power of decision.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: You have a point, Spock?
Mr. Spock: Yes. Always, Doctor. We have here an unusual opportunity to appraise the human mind, or to examine, in Earth terms, the roles of good and evil in a man: his negative side, which you call hostility, lust, violence, and his positive side, which Earth people express as compassion, love, tenderness.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: It's the captain's guts you're analyzing. Are you aware of that, Spock?
Mr. Spock: Yes, and what is it that makes one man an exceptional leader? We see indications that it is his negative side which makes him strong, that his "evil" side, if you will, properly controlled and disciplined, is vital to his strength.
Mr. Spock: Your negative side removed from you, the power of command begins to elude you.
Captain James T. Kirk: What is your point, Mr. Spock?
Mr. Spock: If your power of command continues to weaken, you'll soon be unable to function as captain. You must be prepared for that.
Sulu: Temperature's starting to drop?
Captain James T. Kirk: Yeah. At night it gets down to 120 degrees below zero.
Sulu: That's nippy.
Wilson: What happened?
Fisher: I took a flop.
Wilson: Onto what?
Fisher: I don't know. Some kind of yellow ore.
Scott: A few seconds after they sent this one up through the transporter, that duplicate appeared. Except it's not a duplicate. It's an opposite. Two of the same animal, but different. One gentle: this. One mean and fierce: that. Some kind of savage, ferocious opposite. Captain, we don't dare send Mr. Sulu and the landing party up. If this should happen to a man...
Captain James T. Kirk: All hand phasers must be set on base cylce. Stunning force. The imposter is not to be injured. Use minimum force.
Sulu: Can you give us a status report, Captain? Temperature's still dropping. Now 41 degrees below zero.
Captain James T. Kirk: We've located the trouble. It shouldn't be much longer.
Sulu: Do you think you might be able to find a long rope somewhere and lower us down a pot of hot coffee?
Captain James T. Kirk: I'll see what we can do.
Sulu: Rice wine will do if you're short on coffee.
Sulu: I think we ought to give room service another call. That coffee's taking too long.
Sulu: We're using hand phasers to heat the rocks. One phaser quit on us, three still operating. Any possibility of getting us back aboard before the skiing season opens down here?
Captain James T. Kirk: Help me. Somebody... make the decision.
Mr. Spock: Are you relinquishing your command, Captain?
Captain James T. Kirk: No. No, I'm not.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: Well, then, we can't help you, Jim. The decision is yours.
Sulu: Enterprise, this is Sulu.
Captain James T. Kirk: Kirk here, Mr. Sulu.
Sulu: Hot line directly to the Captain. Are we that far gone?
Captain James T. Kirk: I gave everybody the afternoon off. I'm watching the store.
Scott: Uh, it might profit ya to let Dr. McCoy give ya the once-over.
Captain James T. Kirk: All right, engineer, I'll have my engines looked to.
Captain James T. Kirk: Yes, Mr. Spock, what is it?
Mr. Spock: Is there something that I can do for you, Captain?
Captain James T. Kirk: Like what?
Mr. Spock: Well, Dr. McCoy seemed to think I should check on you.
Captain James T. Kirk: That's nice.
Captain James T. Kirk: [talking about Kirk's "negative" side-duplicate] I have to take him back... inside myself. I can't survive without him. I don't want to take him back. He's like an animal, a thoughtless, brutal animal, yet it's me... me.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: Jim... you're no different than anyone else. We all have our darker side. We need it! It's half of what we are. It's not ugly. It's human.
Captain James T. Kirk: Human.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: Yes, human. A lot of what he is makes you the man you are. God forbid I should have to agree with Spock, but he was right. Without the negative side, you wouldn't be the captain - you couldn't be, and you know it. Your strength of command lies mostly in him.
Captain James T. Kirk: What do I have?
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: You have the goodness.
Captain James T. Kirk: Not enough. I have a ship to command.
Lt. Cmdr. Leonard 'Bones' McCoy, M.D.: The intelligence, the logic. It appears your half has most of that, and perhaps that's where man's essential courage comes from. For you see, he was afraid, and you weren't.