Full Idea
All naturalism in morality, that is all healthy morality, is dominated by an instinct for life.
Gist of Idea
Healthy morality is dominated by an instinct for life
Source
Friedrich Nietzsche (Twilight of the Idols [1889], 4.4)
Book Reference
Nietzsche,Friedrich: 'Twilight of the Idols and The Anti-Christ', ed/tr. Hollingdale,R.J. [Penguin 1972], p.45
A Reaction
Sounds right. There is no reasoning against a moral nihilist, because they seem to have no instinct in favour of life. It is the given of morality.