The banality of evil thesis forced Arendt into a second major project: if thoughtlessness makes ordinary people capable of participating in atrocity, what exactly is thinking, and what makes it a moral safeguard?
Arendt's answer, developed in The Life of the Mind (1978, published posthumously and unfinished), draws on Socrates more than anyone else. Thinking, for Arendt, is not calculating, not problem-solving, not intelligence. It is the inner dialogue of the self with itself, the kind of questioning, examining, and self-confrontation that Socrates modeled. When Socrates says "the unexamined life is not worth living," he is not making a recommendation about intellectual sophistication. He is making a claim about the minimal condition for being genuinely human rather than merely functional.
Arendt identifies two kinds of mental activity that are often confused with thinking but are not:
First, cognition, the goal-directed mental activity of acquiring knowledge and solving problems. You can be enormously cognitively capable, clever, efficient, good at your job, without ever genuinely thinking in Arendt's sense. Eichmann was cognitively competent. He solved logistical problems expertly. He thought about how to transport Jews to death camps. He never thought about whether to.
Second, will, the capacity to make decisions and act on them. Eichmann had will. He decided, acted, executed plans. What he lacked was the thinking that should precede and constrain the exercise of will: the genuine consideration of what is being willed and whether it should be.
Thinking, on Arendt's account, produces judgment, the specific faculty by which we assess particular situations without reducing them to pre-given rules. Kant's Critique of Judgment is Arendt's touchstone here. Judgment is not applying a rule mechanically to a case; it is the capacity to see a particular situation clearly and assess it without the crutch of a formula. This is exactly what bureaucratic systems are designed to eliminate: they replace judgment with procedures, assessment with rule-following, the particular case with the general category.
Arendt's Socratic claim: thinking makes you a harder person to co-opt into evil. Not because it makes you morally superior or more virtuous in a traditional sense. But because genuine thinking inevitably involves confronting yourself, the two-in-one, the internal dialogue, in a way that makes pure obedience very difficult. A person who genuinely thinks about what they are doing cannot remain fully a function of a system. They are always also a person standing in judgment of what the system is doing through them.
This does not mean that thinking people are automatically good. Arendt is not naive about this. Brilliant philosophers supported Nazism (Heidegger is the example she did not quite name but clearly meant). Thinking in the pure cognitive sense is compatible with evil. What Arendt means is something more specific: the thinking that involves genuine self-confrontation, genuine attention to the human reality of one's actions, genuine willingness to judge without procedural cover, this is what Eichmann lacked, and its absence was what made him capable of what he did.