Human responsibility is at the heart of the book’s third and most important essay, “Two Concepts of Liberty.” Human beings can be responsible if and only if they have a certain amount of freedom to determine how they will think and act. Berlin posits that such liberty can be of two sorts. There can be “negative” liberty, which essentially asks the question, “How much can a person be left alone?” Contrasted to this is “positive” liberty, which asks “To what degree can a person influence his surroundings, especially the actions of others?”

Negative liberty is important because all people give up some personal liberty for social order but people must retain a minimum amount of liberty to preserve their humanity. The more a person is uncommanded by the state, organizations, or others, the more negative liberty he or she retains—in other words, the more the individual is left alone. The concept and practice of negative reality are most important in dealing with the modern state, which has increasingly sought to control the behavior of its citizens. Negative liberty can be a danger when individuals, businesses, or other groups are left free to do actual harm to others, as when industry unregulated by government pollutes rivers or when employers exploit their employees. As Berlin notes, “Freedom for the wolves means death for the sheep.”

Positive liberty comes from the wish of individuals to be their own masters, but it also can lead to a desire to be the master of others. Without a system that provides for checks and balances, this can lead to excessive control, even tyranny. As Berlin notes, positive liberty has more often been perverted than negative liberty, which is why he urges caution.

Both forms of liberty are good and desirable, but both can lead to situations where people desire equally valuable but irreconcilable goals. For Berlin, there is no absolute standard for setting the limits of negative or positive liberty; each society and ultimately each human being must decide where to draw that line.