Perhaps reasonable can be seen as in what is acceptable or not. Values are accepted not in an either/or manner, but partially. I would accept Your such and such only if. There are no absolute truths, values, or the reasoning behind them. What is reasonable for me may not be for You, but in the public domain, reasonable is analogous to general acceptance. How would a reasonable man think, in such and such a scenario?
It is an inference which has to be made, in order to be able to get out of absolute subjectivity. Absolutely subjective values do not exist, even in the minds of the most subjective values. Propositionally, valuless statements such as," I love what I see" , is not absolutely void of meaning, because although, it can be supposed that I see what I love, the fact that I may not see it, doesen't mean I could not love it, would I see it. So there is a possibility involved in nihilism, a possibility of sharing general concepts.
Even a conceptual nihilism, an unshared negation of general concepts, implies a possibility. So nihilism may be a deliberate negation of that possibility, but that negation does not desribe the conceptual negation, only of its usage. We choose not to use that possibility, by disuse. “I love what I see” becomes, "I do not see it, and even if I did, how could you know of my seeing it? You could only rely on the the fact that I am honest in my saying “I see it”
So, even though, there is no certainty that I am lying , there is a possibility that I am telling the truth, and whatever I am seeing ,I love. The possibility of that truthful proposition, leads to upon request, to elaborate as to what exactly I am seeing that I love.
Nihilism is a break in the chain of possibility of reasonabless. Not that that possibility does not exist. What causes the break? The appearant uselesness of a concept lays not in the fact that it is necessarily useless, but that it isn’t useful, now, or it isn’t being used. Usage makes values. Whatever I can use, I keep, whatever I can’t, I throw away. It is not a simple simple nihilism of belief in value and it’s negation.
When Nietzche said “god is Dead” he is not saying god is dead. And before that he was alive, he is saying --God is of no use.(Not that we can’t use the term, but we don’t know, we can’t know what God is.
The objective use of God is dead, but the possibility of its usage isn’t.
Therefore, nihilism is not a general denial, but of a specific abandonment of it’s reasonable possibility.