"To accomplish his object Ahab must use tools; and of all tools used in the shadow of the moon, men are most apt to get out of order. He knew, for example, that however magnetic his ascendency in some respects was over Starbuck, yet that ascendency did not cover the complete spiritual man any more than mere corporeal superiority involves intellectual mastership; for to the purely spiritual, the intellectual but stand in sort of corporeal relation. Starbuck’s body and Starbuck’s coerced will were Ahab’s, so long as Ahab kept his magnet at Starbuck’s brain."
Musing: Damn, that first line gives me chills. And now I know why we call some people tools! But think about what is being said - Ahab knows that Starbuck is the one person who could get in his way. Ahab also knows Starbuck has to be manipulated and that manipulation must be aimed at his religious beliefs. In the end, Starbuck's religion is what dooms him. So Ahab guessed correctly, I guess. Shivers.