Do you know why you're not afraid to die, Spock? You're more afraid of living. Each day you stay alive is just one more day you might slip and let your human half peek out. That's it, isn't it? Insecurity. Why, you wouldn't know what to do with a genuine, warm, decent feeling.
All S1
S1 E15Unfinished Business
You humans have that emotional need to express gratitude. "You're welcome," I believe is the correct response.
You're a Roman Kirk, or you should have been...Get away Merick, the thoughts of two men cannot interest you...
[Claudius Marcus tells Kirk they reserved 15 minutes on the regular show on TV for Kirk's live execution]
You may not understand because you're centuries beyond anything as crude as television.
FFlavius
At least defend yourself.
I am defending myself!
Need any help, Doctor?
[struggling in gladiator fight] Whatever gave you that idea?
Caesar and Christ... they had them both.
[To Kirk] Without facts, the decision cannot be made logically. You must rely on your human intuition.
GSGary Seven
That, Miss Lincoln, is simply my cat.
Roberta [sceptical]: Your cat? [She turns back to Isis, who briefly turned into a human woman, and there indeed is a black cat]
His brain is gone.
KKara
Brain and brain — what is brain?!
No one may kill a man. Not for any purpose. It cannot be condoned.
Captain, there is a definite pleasurable experience connected with the hearing of your voice.
I knew it was wrong, I shouldn't have done it.
What's that?
I should have never reconnected his mouth.
It would be illogical to assume that all conditions remain stable.
These quotes come from Wikiquote's Star Trek: The Original Series pages and are available under the Creative Commons Attribution-ShareAlike License.