My readings aside - concerned with philosophy, to say nothing of science, in which I had developed a lively interest - one mental discipline was instrumental in acquiring the insights necessary to write about the human nature: self-observation. This discipline yielded self-knowledge that was relevant to this nature inasmuch as my individuality was human and my humanity universal. The verification of this relevance was to be performed first by myself, who could compare my thinking with that of experienced and educated minds before being published, then by readers, who no less than writers were the gatekeepers of truth.

Just as researchers, in pursuit of objectivity, tested the hypotheses of other researchers by means of their own experimentation, knowledge, and reasoning, readers could support or challenge my statements on the basis of their personal experiences, studies, and reflections.

These experiences and related reflections, like this experimentation and related reasoning, were of prime importance since they constituted a direct and intelligent grasp of reality, indispensable to the evaluation of theoretical thinking. Moreover, since time immemorial throughout the world, the direct and intelligent grasp of reality had been the heart of knowledge, without which studies could never have existed for want of a content. It even was the raw material behind the fanciful aspects of primitive knowledge, which included an array of projections, such as the act of ascribing human characteristics to universal forces.

Having said that, no one could know everything firsthand, from facts versus from statements. This was especially true as regards history and science. Their objects of study usually belonged to the distant past and were treated by historians who relied on a variety of olden archives and chronicles, or they belonged to the present but were often small or far in the extreme, open to observation by scientists who had special instruments like microscopes and telescopes at their disposal.

By contrast, in the field of philosophy, with particular reference to generalities derived from common realities, there was no excuse for subscribing blindly to the affirmations of others. One had the freedom, even the duty, to investigate them both empirically and rationally to estimate their level of conformity or applicability to these realities. In the end, one had to use one’s own judgment and form one’s own opinion, which was bound to disagree in some ways with other ones. Human limitations and fallibility were a source of relativity and oppositions.