Autonomy
Enlightenment, as Kant defines it, is about thinking for oneself rather than relying on external help. In this sense, enlightenment means achieving intellectual autonomy. Individuals who remain unenlightened refuse to achieve autonomy and remain dependent in thought, which keeps them in a state of immaturity. An autonomous person, on the other hand, is able to exercise her own reason. She can choose what to believe instead of blindly obeying the church; she can choose what to eat for herself without having a physician decide on her behalf; she can think and understand independently as a free agent. Once autonomy is attained, one requires no more guidance from others and becomes intellectually mature, and therefore, enlightened.
Nature
Kant’s strong faith in enlightenment is rooted in a view of nature. He believes that enlightenment is inevitable, as it is the natural progress of mankind. If not intentionally held in a state of immaturity, people will emerge out of it spontaneously. Humans are given the capability of thinking on their own, and once the restrictions are lifted, they will realize their natural potential. Enlightenment is developed and advanced by a natural force. Thus, it is impossible to halt the process of enlightenment. Any attempt to restrict it is a crime against human nature.
Freedom
According to Kant, freedom is the only thing required to bring about enlightenment. However, not all freedoms should be unrestricted; only the "harmless" kind—public freedom—should remain unfettered. Kant differentiates between public and private freedom. Public freedom pertains to the liberty to express one’s opinion in public spaces, addressing a universal audience, as one does in the press. When people have the freedom to use their reason publicly, enlightenment is inevitable. In contrast, private freedom refers to liberties one holds in one’s professional role. While private freedom should be restrained, public freedom should be unbridled. When public freedom flourishes, a handful of individuals will first achieve independence. Acting as trailblazers, they will inspire enlightenment throughout society.
Optimism
Kant’s advocacy for the unfettered freedom to exercise one’s reason implies an optimism about reason. It first expresses a faith in the capacity of reason, such that humans are able to grasp truth without the guidance of religion. This perspective resonates with the ethos of the Enlightenment era, which was characterized by a new confidence in the human intellect, inspired by scientific discoveries. For Kant, humans can reason, and reason well. They are capable of understanding. Kant’s argument for the freedom to exercise reason fully also reflects his expectation that unassisted reasoning does not promote undesired outcomes such as libertinism.
