Metaphysics studies the basic elements of existence. The field of metaphysics immediately divides into two sub-fields: ontology, which studies the basic categories of existence; and modality, which studies the nature of necessity and possibility. Nietzsche has a lot to say about both ontology and modality, and what he has to say about each is fascinating albeit in the end incomplete and fragmentary. As we should expect, Nietzsche has no patience for the views of most metaphysicians. He calls himself a “godless anti metaphysician” (GS 344), and for good reason; as far as he is concerned, the history of metaphysics is a heritage of bogus explanations, fictitious entities and erroneous causes. This is not to say that Nietzsche thinks that metaphysical explanations of phenomena are not seductive. The worldwide success of religion attests to the contrary that they are. Nietzsche's assessment of that attraction is twofold. First, he thinks that metaphysics is a juvenile pastime indulged because it makes “meaningful … things that [one] found unpleasant or contemptible” (HAH I 17). But this jejune interest is, eventually, discarded and replaced with history and science. The second reason is more general and more pernicious. Nietzsche thinks that many of us share a set of assumptions that force us into compliance with metaphysical claims. These assumptions are “in the last resort the spell of physiological value judgements” (BGE 20) that life is not worth living and they work together to form the “theological instinct” or the philosophical “idiosyncracy” (TI III 1) of being fundamentally queasy with transience, change, power, life and suffering.