Appendix 12. - (fn. 135)

If in Bossuet's time some scholar had appeared who, instead of taking a different road from that into which philosophy had been directed by Descartes, had chosen solely to move it forward along the same route, to be magnanimous in welcoming and preserving truths which had already been explained, to verify them and add to them, he could have developed this opinion without departing greatly from what was then known. Merely by bringing together and clarifying such truths, he would have brought great benefit to philosophy. This development might have run as follows.
The intellect was defined as 'the faculty of knowing what is true and what is false.' It only remained, therefore, to discover what truth and error were. Clarifying this would have brought philosophy an endless benefit, and could have been done, as I said, without venturing too far from knowledge already possessed.

In fact, Bossuet defined what is true and what is false as follows: 'The truth is what is, error is what is not' (chap. 1: 16). According to Bossuet, therefore, truth is ens. The intellect is thus simply the faculty by which we perceive ens, as Bossuet himself says.
Along these lines, it was necessary to endeavour to demonstrate carefully that
1. Sense perception could in no way grasp ens (cf. 52-62) but only the things accidental to ens.
2. This idea must consequently have been planted within us by nature (cf. 51).
3. Substances are perceived by the perception of ens itself.
4. Substances are therefore perceived by our intellect alone (cf. 48-50).
5. The idea of ens shorn of all the determining factors coming through the senses is the most individual idea of all.
6. All other ideas receive their character of universality from the idea of ens.
7. All ideas are furnished with this characteristic which constitutes the nature of ideas (cf. 90-98).

Finally, we would have learned and established that the intellect is not only 'the faculty of what is true and false' but that it alone is 'the faculty of ideas', which cannot pertain to the senses. In brief, all the truths which I have tried to expound in this work could have been elucidated step by step.