 The main idea is clarified in Russell 1908 (pp. 163–164) by considering how propositions can be arranged into a suitable “ramified” hierarchy, according to their order and so as to satisfy the vicious circle principle. First of all, there are elementary propositions, i.e., those containing no bound variables at all, while the lowest type consists of individuals. Individuals are entities without logical structure and can be regarded as the subjects of elementary propositions. The second logical type embraces the first order propositions, i.e., those whose quantifiers (if any) range only over individuals. Quantification over first order propositions gives rise to a new type, consisting exactly of second order propositions. In general, the \((n + 1)\)th logical type comprises propositions of order \(n\), which contain quantification only up to the \((n - 1)\)th order.