objections applicable to all the demonstrations.
IX
Burali-Forti has given another demonstration.1616 But he is obliged to assume two postulates: First, there always exists at least one infinite class. The second is thus expressed:
The first postulate is not more evident than the principle to be proved. The second not only is not evident, but it is false, as Whitehead has shown; as moreover any recruit would see at the first glance, if the axiom had been stated in intelligible language, since it means that the number of combinations which can be formed with several objects is less than the number of these objects.
X
Zermelo's Assumption
A famous demonstration by Zermelo rests upon the following assumption: In any aggregate (or the same in each aggregate of an assemblage of aggregates) we can always choose at random an element (even if this assemblage of aggregates should contain an infinity of aggregates). This assumption had been applied a thousand times without being stated, but, once stated, it aroused doubts. Some mathematicians, for instance M. Borel, resolutely reject it; others admire it. Let us see what, according to his last article, Russell thinks of it. He does not speak out, but his reflections are very suggestive.
And first a picturesque example: Suppose we have as many pairs of shoes as there are whole numbers, and so that we can number the pairs from one to infinity, how many shoes shall we have? Will the number of shoes be equal to the number of pairs? Yes, if in each pair the right shoe is distinguishable from the left; it will in fact suffice to give the number 2 n − 1 to the right shoe of the n th pair, and the number 2