Final answer:
Thomas Aquinas believes that although humans can achieve a form of natural happiness through virtue and reason, perfect happiness requires divine grace. Aquinas's perspective is grounded in the concept of natural law theory, which posits an objective moral order but also recognizes that full human flourishing is ultimately dependent on the divine.
Step-by-step explanation:
According to the medieval philosopher Thomas Aquinas, humans cannot achieve ultimate happiness through their own natural powers alone. For Aquinas, happiness or eudaimonia is the ultimate end of human actions and is associated with living in accordance with virtue. However, he differentiates between a natural happiness achievable through human reason and a supernatural happiness that transcends human nature and requires divine grace. Natural happiness can be pursued through the exercise of virtue and adherence to the natural moral order, which Aquinas believes is derived from God's eternal law. Yet, this natural happiness is limited and imperfect. The perfect happiness, which is the beatific vision of God, is beyond natural human capacity and can only be granted by God's grace.
Aquinas also uses the concepts of potentiality and actuality, echoing Aristotle, to explain how things strive to attain their ultimate form or purpose. While human beings can use reason to understand natural laws and to cultivate virtues that enable them to achieve a form of happiness, this is still not the perfect happiness that comes from union with God according to Aquinas's perspective.
Furthermore, Aquinas outlines natural law theory, which posits that there is an objective moral order grounded in the inherent nature of humans. This view, alongside divine law, suggests that while human reason can discern the natural law and humans can strive for goodness, they still fall short of achieving the highest form of happiness without divine aid. Critics of natural law theory argue that the complex nature of human behavior and environmental influences makes it difficult to deduce moral principles solely from human nature. They suggest human behaviors are not as deterministically guided by nature as with other species such as cats or lions.
In summary, for Aquinas, while the cultivation of virtues and adherence to the moral order can lead to a form of happiness, the full glory of human happiness as union with God cannot be attained by natural means alone, but rather by the grace of the divine.