Explain Aquinas’ development of the idea of natural good in Natural Law Ethics.

St Thomas Aquinas develops his idea of the natural good based, primarily, on the foundational principle that all things made by God have a purpose, or 'telos.' This principle was first theorised by Aristotle and then subsequently developed by Aquinas in the Middle Ages. Aquinas stated that the principle of 'telos' was bestowed on humanity through creation, at the hands of the God of Christianity. To fulfil one's purpose is therefore a good, as it is fulfilling the eternal and divine law of God. Aquinas developed the idea of Natural good by suggesting that through the use of our innate, universal reason we can discern and discover these goods in order that we can work to achieve them - thus fulilling our 'telos.' Through the use of God-given reason we can discern our natural inclinations, or basic goods, and from these basic goods we can discover our primary and secondary precepts that allow us to fulfill our purpose. For example, the basic good is to do good and avoid evil. From this good a primary percept can be discovered (through reason) which would be to educate children, and a secondary precept would follow, such as do not abort an unborn child. According to Aquinas, the use of correct practical reason will lead to the precepts that allow us to fulfill our purpose; namely the preservation of life and the continuation of the species through reproduction, and they are goods because they are natural. The misuse of reason will lead to apparent goods which will inevitably lead to a sinful act. For Aquinas the supreme good was union with God. For Aristotle it was eudaimonia.