Of the four branches of practical ethics, individual morality – in which man is treated as though living an isolated life, having no relationships with others – is the most elementary. So natural is individual morality that we needn't go to great lengths to establish its importance. Insofar as man is isolated, either in fact or in principle, what duties does he owe to himself?

To answer this question, we need only apply to this particular case the general formula of the moral law. Man must treat his personality as an end and never as a means. In other words, he must always respect and develop his personality, never allowing it to become a means to some other end; assure himself that everything within him might be perfected; and then try to achieve this perfection. Now, man has both a body and a soul, and the two are closely connected. So let's begin by asking: What are our duties to our body?

The first is to preserve it. We have no right to take our own lives. Suicide is immoral for three reasons:

1. We have duties that must be fulfilled. Even in the hypothetical situation in which man is isolated, we're duty-bound to develop our intelligence, sensibility, and activity. Killing ourselves makes it impossible to perform these duties.

2. […]