 The Vicious-Circle Principle serves, nevertheless, as an effective motivation for a particular account of legitimate concepts and definitions, namely that embodied in Russell’s Ramified Type Theory. The idea here is that one begins with some unproblematic resources that involve no quantification over propositions, concepts, and such. These resources enable one to define, for example, various unary concepts, which are thereby assured of satisfying the Vicious-Circle Principle. Quantification over these concepts is thus bound to be legitimate, and can be added to the language. The same holds for propositions and for concepts falling under other types: for each type, a quantifier can be added that ranges over items (of that type) that are definable using the initial unproblematic resources. The new quantificational resources enable the definition of further items of each type; these, too, respect the Principle, and again, quantifiers ranging over the expanded totalities can legitimately be added to the language. The new resources permit the definition of yet further items. And the process repeats. The result is that we have a hierarchy of propositions and of concepts of various orders. Each type in the type hierarchy ramifies into a multiplicity of orders. This ramification ensures that definitions formulated in the resulting language are bound to respect the Vicious-Circle Principle. Concepts and classes that can be defined within the confines of this scheme are said to be predicative (in one sense of this word); the others, impredicative.