Aristotle was one of the most influential philosophers who ever lived. His work spans across nearly every field of philosophy and science. He pioneered systematic thinking across logic, physics, biology, ethics and politics. His work reflects a lifelong pursuit to understand how knowledge works, how the world works, and how we should live.

Aristotle lived during the golden age of Athens. He was mentored by Plato at the Academy for 20 years before founding his own school, the Lyceum. Unlike Plato, Aristotle grounded his philosophy in systematic observation and critical thinking. He insisted that knowledge must be built up systematically from experience, not intuited from abstract reasoning alone.

Metaphysics: The Study of Being Qua Being

Aristotle’s metaphysics represents one of the most ambitious attempts in Western philosophy to understand the fundamental nature of reality. At the core of his metaphysics is the study of being qua being—an investigation into what it means for something to exist.

For Aristotle, beings can be spoken of in many ways, but there is a primary sense of being as substance. Substances are independent existences that are the subjects of change and the bearers of attributes. They are neither universal nor particular, but occupy a unique metaphysical position. Substance is form, not matter, since form is what makes matter a definite actuality.

In studying being, Aristotle rejects Plato’s theory of transcendent Forms, arguing that Forms cannot sufficiently explain causation, change and individual substances. Against materialists, he posits formal and final causes alongside material and efficient causes. And he argues that there cannot be a single science of being, since being is not a univocal concept. Yet there can be a science of being qua being that studies beings in their fundamental substantiality.

Aristotle’s approach is driven by a deep confidence in the powers of reason, a refusal to doubt the reliability of the senses, and a search for metaphysical truths grounded in an empirical study of the natural world. He begins philosophical inquiry by laying out the appearances (phainomena) and reputable opinions (endoxa) about puzzles (aporia) that call for explanation. Though not beholden to preserve them, he seeks to explain the world in a way that accounts for significant phainomena.

This search for intelligible explanatory causes leads Aristotle to recognize four fundamental types of aitia or causes—material, formal, efficient and final. Complete explanation requires citing all four causes. His hylomorphism, which posits that material particulars are compounds of matter and form, becomes a central framework for explaining change, nature and human psychology.

With substance established as the primary sense of being, Aristotle’s metaphysics lays a groundwork for his natural philosophy, philosophy of mind, ethics and other areas of inquiry. It represents an enormously ambitious attempt to uncover the basic structure of reality through reasoned analysis.

Epistemology: The Foundations of Knowledge

Aristotle’s epistemology centers on the role of scientific knowledge (episteme) and its foundations. Unlike his predecessors, Aristotle develops a systematic study of logic and valid inference, establishing the deductive syllogism as the basis for scientific demonstration.

Demonstration provides scientific knowledge by inferring necessary conclusions from primary premises that capture fundamental causal explanations. These first principles cannot themselves be demonstrated, but are grasped through intellectual intuition (nous).

Aristotle argues we progress from perception to memory and experience, until experience gives rise to universal concepts which allow us to grasp the inductive first principles of science. Though not infallible, our faculties reliably put us in contact with the basic components of the world. Against skepticism, Aristotle has confidence we can build genuine knowledge on the data of the senses.

Below scientific demonstration, Aristotle recognizes a second mode of reasoning—dialectic. Dialectic deals in endoxa or reputable opinions, rather than necessary premises. Though lacking the certainty of science, dialectic enables philosophical inquiry and ethical reasoning in domains where absolute proof is unattainable. The philosopher begins by surveying endoxa and puzzles (aporia) to help determine principles and move toward truth.

Aristotle’s epistemology represents a foundationalist approach, grounded in his broader metaphysics and natural philosophy. It centers on the discovery of intelligible first principles that are innate in nature and explain the causal order of the world. Combined with logic and dialectic, these provide a framework for systematically building genuine human knowledge.

Ethics and Politics: The Human Good

At the foundation of Aristotle’s ethics is the argument that the highest human good is eudaimonia or happiness, achieved through a life of virtue and excellent rational activity. But virtue consists not in outward behavior, but in having a stable inner character that pursues the mean between extremes.

The ethical virtues are dispositions to feel and act in ways that hit this mean—e.g. courage is the mean between cowardice and recklessness. But ethical virtue on its own is not sufficient. To achieve full excellence, reason must rule by means of the intellectual virtues like practical wisdom, contemplation and theoretical wisdom. The peak of human fulfillment is thus the philosophical life.

Politics for Aristotle is a natural outgrowth of ethics, since our fulfillment requires living in a polis that cultivates virtue and aids our pursuit of the good life. The best political order pursues these goals through a mixed constitution balancing different elements. Aristotle rejects radical democracy in favor of governance by virtuous, property-owning citizens pursuing the common advantage.

At the heart of Aristotle’s ethics is a vision of human beings fulfilling our nature by developing our distinctively human capacities of reason, speech and social cooperation. His empirically-grounded teleology holds up rational virtue as our highest good in both action and contemplation. By linking ethics to politics, Aristotle articulates a positive vision of a society ordered toward human flourishing.

Philosophy of Mind: The Soul as Form

Aristotle’s philosophy of mind grows out of his metaphysical framework. He rejects a Platonic dualism that would make mind entirely separate from body. Instead, the soul is the form of the body—its organizing life principle. Soul and body are thus inseparable, as form and matter.

The somatic soul comprises the nutritive, sensitive and desiderative faculties found in all living things. But humans also possess a rational soul, capable of thought, reasoning and intellectual knowledge. Though relying on the body and its senses, intellectual reason transcends materiality.

For Aristotle, all cognition involves receiving the form of an object without its matter. Sensation receives the form of a sensible object, while intellectual thought receives the form of an intelligible object. The active mind abstracts intelligible forms from phantasms or images in the sensory imagination.

While Aristotle’s philosophy of mind is fundamentally hylomorphic, he cannot fully explain the interaction between immaterial thought and the body. Still, by rejecting Platonic dualism and recognizing the soul’s intrinsic connection to biological life, Aristotle offers an account that deeply influences later thought and remains viable today.

Aristotle’s Legacy: A Philosophy for the Ages

Aristotle’s writings had an immense influence shaping philosophical thought in the ancient and medieval eras. Thinkers as diverse as Plotinus, Augustine, Aquinas, Averroes and Maimonides drew extensively from Aristotle. While not without its critics, Aristotelianism represented the dominant school of Western philosophy for centuries.

With the rediscovery of his works spurring new interest, Aristotle became a central guiding force for Western philosophy through the Renaissance and Early Modern period. Despite fractures caused by the Scientific Revolution and Enlightenment rationalism, Aristotle’s writings remained foundational across theology, ethics, metaphysics and logic.

Even contemporary philosophy, for all its development and critique, still engages deeply with Aristotle’s ideas on an enormous range of topics. Virtue ethics sees renewed interest, while Aristotle’s metaphysics, philosophy of mind, aesthetics, rhetoric and poetics continue to garner attention.

That Aristotle’s works have helped shape millennia of human thought testifies to their enduring insight. Whatever its flaws, Aristotle’s philosophy represents an unparalleled systematic attempt to give rigorous intellectual expression to our most foundational human experiences and intuitions. By thoughtfully engaging Aristotle, we engage part of what it has meant for countless generations to think philosophically about the world.