 In a famous essay first published in 1958, Isaiah Berlin called these two concepts of liberty negative and positive respectively (Berlin  1969).[1]  The reason for using these labels is that in the first case liberty seems to be a mere absence of something (i.e. of obstacles, barriers, constraints or interference from others), whereas in the second case it seems to require the presence of something (i.e. of control, self-mastery, self-determination or self-realization). In Berlin’s words, we use the negative concept of liberty in attempting to answer the question “What is the area within which the subject — a person or group of persons — is or should be left to do or be what he is able to do or be, without interference by other persons?”, whereas we use the positive concept in attempting to answer the question “What, or who, is the source of control or interference that can determine someone to do, or be, this rather than that?” (1969, pp. 121–22).