Criticisms of Thomas Aquinas

Thomas Aquinas (1225-1274) is undoubtedly one of the most influential thinkers in the history of Western philosophy and theology. His integration of Aristotelian philosophy with Christian theology in his magnum opus, the “Summa Theologica,” has had a lasting impact on Christian thought and Western philosophy more broadly. However, his ideas have not been without criticism. Below, we will delve into some of the principal critiques of Aquinas’s philosophical and theological views.

1. Critiques of the Five Ways Aquinas’s Five Ways, his arguments for the existence of God, have been widely debated and criticized. These arguments, based on motion, causation, contingency, degrees of perfection, and the order of the universe, all conclude with the existence of a divine, uncaused cause or mover. One common criticism is that even if these arguments successfully prove the existence of a first cause or mover, they do not necessarily prove the existence of the God of classical theism – a being who is all-good, all-knowing, and all-powerful. David Hume, the Scottish Enlightenment philosopher, argues that the cause of the universe could be very different from the God of classical theism. Another criticism, particularly directed at Aquinas’s cosmological argument (based on causation), questions his assumption that an infinite regress of causes is impossible. Some philosophers and scientists argue that there is no logical or empirical reason to reject an infinite series of causes and effects.

2. Critiques of Natural Law Theory Aquinas’s natural law theory, which posits a moral law known through reason and inherent to human nature, has also received significant criticism. One critique, often associated with legal positivism, holds that law and morality are separate domains. According to this perspective, laws are social constructs and do not inherently possess moral value. Thus, they reject Aquinas’s claim that “an unjust law is not a law.” Additionally, the natural law theory’s reliance on a specific understanding of human nature opens it to criticism. It assumes a fixed human nature, which undergirds moral laws that are universal and unchanging. Critics argue that our understanding of human nature is culturally and historically conditioned and thus may change over time. Therefore, it is not a reliable basis for determining moral law.

3. Critiques of the Integration of Philosophy and Theology Aquinas’s project of integrating Aristotelian philosophy with Christian theology, sometimes called “Scholasticism,” has faced criticism on several fronts. Some Christian thinkers argue that Aquinas grants too much authority to human reason in matters of faith, thus diluting the transcendence and mystery of God. On the other side, some secular philosophers object to the incorporation of theological assumptions into philosophical argumentation. They argue that philosophical claims should be justified by reason and evidence, not religious doctrine.

4. Critiques from Modern Science Finally, Aquinas’s views on the natural world, influenced by Aristotelian science, have been challenged by modern science. Aquinas’s cosmology, his understanding of life forms, and his belief in a hierarchical universe have all been rendered obsolete by contemporary physics, biology, and astronomy. For example, Aquinas’s argument from design, which sees the order and purpose in the universe as proof of a divine designer, has been critiqued in light of Darwin’s theory of evolution. Natural selection provides an alternative explanation for the complexity and functionality of biological organisms, without recourse to a designer.


While Aquinas’s thought continues to have a significant influence, the critiques outlined above demonstrate that his ideas are not without their challenges. Engaging with these criticisms allows for a deeper understanding of Aquinas’s thought and its place within the broader historical and intellectual context. It’s important to remember that like all thinkers, Aquinas was a product of his time, and his work reflects the scientific and philosophical understanding of the world available during the Middle Ages. Despite these critiques, Aquinas’s work remains a cornerstone of Western philosophical and theological thought. His emphasis on rational inquiry into philosophical and theological questions, his systematic approach to ethics and law, and his effort to reconcile faith with reason have left an indelible mark on subsequent thinkers. However, the criticisms directed at his ideas underscore the dynamic nature of philosophical inquiry, where no idea is beyond questioning and revision.

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