In this connection Father Sogol had described to us some experiments he had done a few years before with the idea of measuring the power of human thought. I shall repeat only the parts I could grasp. At the time I wondered how literally one should take it all, and forever preoccupied with my favorite field of study, I admired Sogol as an inventor of 'abstract symbols' (in other words, an abstract thing symbolizing a concrete thing, the reverse of the normal order). But since then I have found that these notions of abstract and concrete have no great significance, as I should have learned reading Xenophon of Elis or even Shakespeare: a thing either is or is not, and that's the end of it. Well, Sogol had tried to 'measure thought'; not the way psychotechnicians and testing experts go at it, limiting themselves to comparing the way one individual performs a certain activity (often, moreover, entirely alien to thought) to the average performance of other individuals of the same age. He was intent on measuring the power of thought as an absolute value.

'This power,' Sogol said, 'is arithmetical. In reality every thought represents a capacity to grasp the divisions of a whole. Now, numbers are nothing else than a division of unity, which is to say, the divisions of any whole whatever. In myself and in others I began to observe how many numbers a man really can conceive, that is to say, can carry in his mind without breaking them down or writing them out; how many successive consequences of a principle he can grasp at once, instantaneously; how many inclusions of species within genus; how many relations of cause to effect, of means to end. And I never found the number to be greater than four. And moreover, this figure four required an exceptional mental exertion which I obtained very rarely. The thought of an idiot stops at one, and the ordinary thought of most people goes to two, sometimes to three, very rarely to four. If you like, I'll summarize one or two of these experiments for you. Follow me carefully.'

To understand what follows, one must perform the proposed experiments in good faith. It requires considerable attention, patience, and serenity of mind.

He went on as follows:

'Represent to yourself simultaneously the following facts:

1. I get dressed to go out;
2. I go out to catch a train;
3. I catch the train to go to work;
4. I go to work to earn a living.

Now try to add a fifth step, and I am sure that at least one of the first three will vanish from your mind.'

We performed the experiment; he was right, and even a little too generous.

Take another type of sequence:

1. the spaniel is a dog;
2. dogs are mammals;
3. mammals are vertebrates;
4. vertebrates are animals. . .