ABSTRACT
C . R U L E S O F C O N SE Q U E N C E F O R L A N G U A G E II
One of the chief tasks of the logical foundation of mathematics is to set up a formal criterion of validity, that is, to state the neces sary and sufficient conditions which a sentence must fulfil in order to be valid (correct, true) in the sense understood in classical mathematics. Since Language II is constructed in such a way that classical mathematics may be formulated in it, we can state the problem as that of setting up a formal criterion of validity for the sentences of Language II. In general, it is possible to dis tinguish three kinds of criteria of validity.
