The Natural Law ethic comes from Aristotle's philosophy.

Proportionalism as an ethical theory is a relatively new theory which tries to bridge the gap between the traditional Christian Natural Law ethic and the modern relativist Christian ethic, Situationism.

Thomas Aquinas' Natural Law ethic is grounded in this principle in that observing the 'end' or 'purpose' (telos) of an organism is the key to unlocking morality in the present moment.