Desire and dissatisfaction › From a body to a world of striving

The bodily argument has two stages that should be kept distinct. In §18 Schopenhauer claims a double knowledge of one's body: it is represented as an object and directly experienced as willing. The act of will and the action of the body are the same occurrence known in different ways. This is intended to identify two aspects of one event, rather than explain how a mental cause pushes physical matter.

In §19 he extends this key beyond his own body. Other things are known externally as representations. He proposes understanding their inner nature by analogy with the one case to which we have inward access. A plant turning toward light and a person reaching for food differ greatly in cognition; the proposed commonality is striving, not conscious decision-making.

The extension is the vulnerable step. An analogy from embodied experience can make a metaphysical interpretation intelligible without proving that every natural phenomenon has the same essence. Schopenhauer argues for the interpretation in the second book, but the reader should not confuse the familiar experience of bodily effort with direct acquaintance with the inner nature of gravity.

His claim that will is one also needs qualification (§23). He does not mean that it is one item alongside other items that could be counted. Counting distinct individuals depends on the forms of appearance, especially space and time. His proposed will lies outside the conditions that make plurality applicable. This is a metaphysical account of individuation, not a discovery that bodies cease to be distinct physical objects.

The conflict among living beings consequently acquires a disturbing interpretation: one underlying reality confronts itself through different individuals. An individual's advantage can come at another's expense. Yet that interpretation does not establish that every human relationship is competitive. The ethical sections ask how a recognition of shared suffering could undermine egoism instead.