What we observe is that these doctrines rarely label themselves nihilist (it would be absurd, for instance, for a Christian to self-identify as one). 'Nihilist' is instead most often an accusation levelled by one author against a rival doctrine. In other words, there appears to be no nihilist manifesto in which the doctrine's meaning is clearly articulated and claimed as one's own.
It seems odd, then, to give credence to a notion that almost no one claims as their own, and which functions more as an insult than as a concept with genuine substance.
Moreover, the definitions of nihilism just surveyed do not form a coherent concept; rather, they associate it with other doctrines whose meanings are far clearer—Christianity, pessimism, or scepticism, for instance.
One is left wondering what additional meaning the term 'nihilism' genuinely offers, and whether it might be no more than an empty shell, lacking any meaning of its own.

I now propose to examine the association of nihilism with pessimism and scepticism, in order to assess whether it has any legitimacy.

b) Is Nihilism a Form of Pessimism?

In his fundamental study of nihilism, Nietzsche appears to equate it with pessimism. By pessimism I mean the axiological doctrine that holds that nothing regarded as having value truly does, giving rise to feelings of sadness, malaise, and perhaps suicidal despair.
Nietzsche in fact addresses the relationship between these two positions directly: he treats one as an essential stage of the other: Pessimism as a preliminary form of nihilism ¹.

This idea rests on two arguments.

First, it is the classic feelings associated with pessimism, as noted above, that nihilism provokes. Chief among these is weariness—the sense that everything is in vain: A glimpse at man nowadays makes us tired—what is contemporary nihilism, if it is not that?... We are weary of man… ².
Second, there is the prospect of outright suicide: Nihilism does not only contemplate the "in vain!" nor is it merely the belief that everything deserves to perish: one helps to destroy. […] The reduction to nothing by judgment is seconded by the reduction to nothing by hand ³.

Nietzsche also identifies three causes for the formation of nihilism in the human mind, each of which connects back to pessimism.

The first is the realisation that the universe has no meaning: Now one realizes that becoming aims at nothing and achieves nothing ⁴, which leads to the recognition of the long waste of strength, the agony of the "in vain" ⁵ (die Qual des Umsonst).
In the second stage, we cease to believe that the multiplicity—or rather the chaos—of being can be subsumed under a unity through which man might rediscover his connection to the Whole, and thereby find value: At bottom, man has lost the faith in his own value when no infinitely valuable whole works through him; i.e., he conceived such a whole in order to be able to believe in his own value ⁶.
Finally, we come to realise that what we took to be truth, what we regarded as the true world, is nothing but a fiction.

With the dissolution of the three categories on which, according to Nietzsche, all value rests—purpose, unity, and truth—value itself dissolves, and man becomes nihilistic: The feeling of valuelessness was reached with the realization that the overall character of existence may not be interpreted by means of the concept of "aim," the concept of "unity," or the concept of "truth." […] Briefly: the categories "aim," "unity," "being" which we used to project some value into the world—we pull out again; so the world looks valueless ⁷.
This brings man to confront that terrible question: The nihilistic question "What for? ⁸.

As we can see, nihilism aligns so closely with pessimism that any distinction between the two doctrines becomes difficult to sustain: nihilism appears to be a name without independent meaning, interchangeable with pessimism. Nietzsche seems to have arrived at the opposite conclusion: Pessimism is not a problem but a symptom, [its] name should be replaced by "nihilism" ⁹. Yet in practice the result is the same—the content of pessimism is simply reassigned to nihilism, leaving Nietzsche's use of the term without any meaning of its own.

1. The Will to Power, Book 1 European Nihilism, 9
2. On the Genealogy of Morals, I, 12
3. The Will to Power, Book 1 European Nihilism, 24
4. Ibid, 12 A
5. Ibid.
6. Ibid.,
7. Ibid.
8. Ibid, 20
9. Ibid., 38