Blaise Pascal once pointed out in connection with mathematical demonstration that it is impossible to operate only with explicit propositions or definitions, for whenever we seek to define the meaning of something in precise terms we have to make use of other terms which for this purpose must themselves remain undefined. Michael Polanyi has shown that this applies no less to all acts of knowledge whether in everyday life or in rigorous scientific inquiry, for any formal account of what we know rests upon a base of informal undefined knowledge, from which it cannot be cut off without becoming empty and useless. This means that a complete formalisation of knowledge in explicit terms is impossible. A cognate reason for this is to be discerned in the fact that in objective knowledge the realities we seek to know inevitably break through any frame of concepts and statements which we use to describe them even though they are developed under the constraint of those realities. Concepts and statements of this kind do not have their truth in themselves but in the realities to which they refer. Hence if we are to do justice to the integrity and nature of the objects of our knowledge we must discriminate them from our knowing of them, and let them confer relativity upon our concepts and statements about them. Thus in all authentic knowledge we have to take into account an informal undefined knowledge grounded in the inherent intelligibility of what we know and must constantly find appropriate ways of letting it exercise a regulative force in all our explicit formulations of it.