What the two great sages, Laozi and Confucius, know about the Book of Changes can be too deep for many Yi students. Therefore their thoughts on this ancient Chinese classic are often missed even by those who considered themselves scholars of ancient Chinese philosophy.
Over the years, Yi students have tried linking up the Tao Te Ching to the Book of Changes without much success. It will be difficult if we do not know both the profound classics well. Another drawback would be the lack of neidan knowledge and practice.
If we are discerning enough, we may find several chapters in the Tao Te Ching relating to neidan and the Zhouyi. This means that the Book of Changes also contains layers on neidan practice which Laozi and some renowned Neo Daoists know about. But many down the ages do not.
If we look clearly at Confucius’ commentaries on certain lines of hexagrams, we may understand how deep his knowledge on the Book of Changes was. But then if we are not earnest in our Yi studies, we may not know why he interpreted those lines as he did.
As to whether he consulted the Book of Changes on occasions is another story altogether. So far I have not come across any evidence of his Yi consultation(s) in the four Confucian books.
Yet I read of a modern scholar, a fellow Malaysian, claiming that Confucius do not use the nuclear trigrams and the changed hexagram for interpretations. And that those who used them, do not or did not know their Yi studies well.
While I verily agree with the scholar that Confucius’s interpretations of the lines are based on the trigrams, we cannot conclusively determine that nuclear trigrams and changed hexagrams cannot be used for interpretations of Yi consultations, unless we have examples of consultations performed by the great sage, Confucius and his interpretation of them to form such an opinion.
Though my knowledge of the Yi is minimal compared to the two great sages, I do use the nuclear trigrams on occasions to provide more clarity to the prognostications or omens. And I use the changed hexagrams more often than not.
But does this mean that the particular modern scholar know the Yi better than me? Nope. Since down the ages, the Yi has been too deep for many.