Quite similar was the question of classification. Just as we had to take the responsibility for the staking-out of every section, we had also to decide in favor of a certain grouping, if we desired to organize the Congress and not simply to bring out haphazard results. The principles which are sufficient for a mere directory would never allow the shaping of a programme which can be the basis for synthetic work. Even a university catalogue begins with a certain classification, and yet no one fancies that such catalogue grouping inhibits the freedom of the university lecturer. It is easy to say, as has been said, that the essential trait of the scientific life of to-day is its live-and-let-live character. Certainly it is. In the regular work in our libraries and laboratories the year round, everything depends upon this democratic freedom in which every one goes his own way, hardly asking what his neighbor is doing. It is that which has made the specialistic sciences of our day as strong as they are. But it has brought about at the same time this extreme tendency to unrelated specialization with its discouraging lack of unity; this heaping up of information without an outer harmonious view of the world; and if we were really at least once to satisfy the desire for unity, then we had not the right to yield fully to this live-and-let-live tendency. Therefore some principle of grouping had to be accepted, and whatever principle had been chosen, it would certainly have been open to the criticism that it was a product of arbitrary decision, inasmuch as other principles might have been possible. A classification which in itself expresses all the practical relations in which sciences stand to each other is, of course, absolutely impossible. A programme which should try to arrange the place of a special discipline in such a way that it would become the neighbor of all those other sciences with which it has internal relation is unthinkable. On the other hand, only if we had tried to construct a scheme of such exaggerated ambitions should we have been really guilty of anticipating a part of that which the specialistic scholars were to tell us. The Congress had to leave it to the invited participants to discuss the totality of relations which practically exist between their fields and others, and the organizers confined themselves to that minimum of classification which just indicates the pure logical relations, a minimum which every editor of encyclopedic work would be asked to initiate without awakening suspicions of interference with the ideas of his contributors.