A weakness in classical liberalism, and in more ways than one, is its "negative" notion of liberty as freedom from coercion and interference. F.A. Hayek's fullest account of the nature of liberty is in The Constitution of Liberty. In Law, Liberty and Legislation, for example, he refers back to that account, except to modify the basic formula to "the state in which each can use his own knowledge for his own purposes," which, he thinks, is preferable to Adam Smith's "to pursue his own interest in his own way" which has egoistic overtones. Hayek also considers an equal opposite of liberty, namely, oppression, a state of continuous acts of coercion. Coercion can be a single act, and, as such, is not necessarily a deprivation of liberty. What Hayek seeks is a general set of conditions which constitute liberty or its absence and which can be universally applied.