I am fairly certain that Lewis would follow this lead had he said more in answer to this question, and so I will follow it and dare to propose that there are two, possibly even three, senses of “knowing.” First, there is the sense of knowing that something is true. This sort of knowing could be further subdivided into (a) knowing “just the facts” as Joe Friday and Gaius and Titius would think of “the facts” (e.g., that the waterfall is 250 feet tall, with an average flow of 8.4 million gallons per minute), and (b) knowing facts about value (i.e. about a reasonable and proper affection or emotional reaction towards a certain object, event or person). Secondly, there is the sense of knowing the truth of something—the sense of being true to that thing by actually having the appropriate response. What is crucial here is that we actually do use the word “know” in all of these ways; and usually it is clear from the context, expression of voice, and known characteristics of the individuals involved, which sense is intended. (Think of sentences like these: “He talks, but says nothing.” “Some men are not men at all.” “He may be King, but he’s no king.” A friend of mine once said to me, “There’s no such thing as Country Music: if it’s Country, it’s not music.”)
Given these distinctions, there are two senses in which someone might be said to be “within the Tao.” One might be said to be “within the Tao” if one knows that there are proper and improper affections or emotional responses to a variety of objects, events, and persons (1b), and if one therefore seeks to discover and learn what these proper and improper affections or emotional responses are. In the first chapter of The Abolition of Man, Lewis shows clearly what the practical consequences are of not living within the Tao, in this sense: the result is “men without chests,” persons with no spirit, no passion. Such (so-called) men neither love nor hate anything. Then, in the second chapter of The Abolition of Man, Lewis shows that being “outside the Tao” in this sense—i.e., not knowing that there are objectively proper and improper affections or emotional responses to a variety of objects, events, and persons, and therefore determining for oneself what affections or emotional responses are “proper” and “improper”—also has logical consequences: it is self-contradictory. For any attempt to reject or justify any particular set of personally or culturally determined values necessarily presupposes that there are values we all share. Simply put, if all values were merely opinions or matters of taste, we could not (and would not) value them. Such “values” aren’t values. Such “values” are worthless.
So far, so good. And the nihilists agree! “It’s all or nothing: and since we reject all,” they say, “we’ve got nothing left! We always knew moral relativism was weak and pale and suffered from consumption! The only true way is to scrap values altogether. A ‘revaluation of all values’ is what we want; and not because it would be better or worse or advantageous for any such evaluative reasons, but just because we desire it.”
As I mentioned, Lewis demonstrates that the conclusion of this view is the abolition of Man: for without any values, neither objective nor subjective, there can be no (deliberate) choice, no exercise of reason, and no morality. If the nihilists win the day they will have nothing preventing them from imposing whatever kind of conditioning they desire upon others and will rob them of their freedoms. Yet the nihilists themselves will necessarily be enslaved to their own irrational desires and the forces of nature that will sway their moods and condition their reactions. In short, whatever we had, it would not be Man: whatever kind of creature we would be, we would no longer be Men.
Lewis’ demonstration is brilliant and, as far as I can see, unassailable by argument. Nevertheless, the bleak picture he paints might still be unavoidable if the alternative—living within the Tao—turns out to be nonsense. For even if we admit the possibility of knowing facts about value, we’ve still got the circularity to deal with; and the second sense of “knowing.”