On the other hand, a second question arises: is nihilism, whose power of negation affects everything, not similar to scepticism? Is it not a kind of scepticism?

Once again, I believe these two forms of thought are incommensurable. Scepticism doubts the possibility of truth, while nihilism focuses not on the notion of truth, but on the notion of value.
Furthermore, and this is the most important point, the sceptic doubts everything and does not even know if the truth is attainable. Through epoché, he refrains from taking a position; in other words, he neither judges nor affirms. In contrast, nihilism asserts, loud and clear, that nothing has value. It is full of certainty, claiming to represent knowledge.

Thus, we see that nihilism is a unique way of thinking, irreducible to either pessimism or scepticism— a distinction often overlooked in modern thought. It is a distinct mode of thought whose specificity deserves to be understood on its own terms.

Once nihilism is better identified in its theoretical aspect, we then realise there was a philosopher who was explicitly nihilist or at least explicitly displayed the nihilist position. In other words, there is a Manifesto of Nihilism in the history of philosophy, and we can recognise it as such now that we have a clearer understanding of what nihilism is.

Surprisingly, perhaps even extraordinarily, we encounter this philosopher at the very outset of philosophy as both a way of thinking and a way of being: Thales, the first philosopher. In one fragment, we find the following exchange: Death is no different from life he said. So why are you not killing yourself? someone asked. Because, he replied, it makes no difference ¹.
If we take Thales to imply not only an essential identity between life and death but also an equality of value, what conclusion might we draw? Not that Thales was a nihilist. We cannot be certain of this, and it would perhaps be unfair to attribute a thought to him that he may not have held, risking an anachronism. However, Thales expresses, in a particularly clear way, what could be a dialogue with an authentic nihilist: he would not respond differently.

We encounter a similar idea in Cioran, who at times expresses classic pessimistic thoughts, for example: Wouldn't it be better if I buried my tears in the sand on a seashore in utter solitude? But I never cried, because my tears have always turned into thoughts. And my thoughts are as bitter as tears ². Yet, he also develops genuinely nihilistic reflections, for instance: Although life for me is torture, I cannot renounce it, because I do not believe in the absolute values in whose name I would sacrifice myself. If I were to be totally sincere, I would say that I do not know why I live and why I do not stop living. […] Why should I bother? Let death appear in a ridiculous light; suffering, limited and unrevealing; enthusiasm, impure; life, rational; life's dialectics, logical rather than demonic; despair, minor and partial; eternity, just a word; the experience of nothingness, an illusion; fatality, a joke! ³.

Cioran is aware that the traditional responses of pessimism—despair, tears—are of no use to him, as embracing them would imply ascribing value to them, a step his axiological stance prohibits. He senses, albeit vaguely, that he inhabits an entirely different realm from classic pessimism, yet he struggles to find the words to convey the full radicalness of his position: I do not know whether I am desperate or not, since lack of hope does not automatically imply despair. I could be called anything because I stand to lose nothing. I've lost everything! flowers are blooming and birds are singing all around me! How distant I am from everything! ⁴.

At one point, he magnificently links, in the same sentence, the content of nihilism and his awareness of its radical nature: Why don't I commit suicide? Because I am as sick of death as I am of life. I should be cast into a flaming caldron! Why am I on this earth? I feel the need to cry out, to utter a savage scream that will set the world atremble with dread. I am like a lightning bolt ready to set the world ablaze and swallow it all in the flames of my nothingness. I am the most monstrous being in history, the beast of the apocalypse full of fire and darkness, of aspirations and despair. [...] My symbol is the death of light and the flame of death. Sparks die in me only to be reborn as thunder and lightning. Darkness itself glows in me ⁵.

1. Lives and Opinions of Eminent Philosophers, Book 1
2. On the heights of despair, Nothing is important
3. Ibid.
4. Ibid., I do not know
5. Ibid., The monopoly of suffering