Aristotle was born in 384 BCE in Stagira, a small town in northern Greece. His father, Nicomachus, was a physician at the Macedonian royal court, which likely influenced Aristotle’s early interest in biology and the natural world. At the age of 17, Aristotle moved to Athens to study under Plato at the Academy, where he stayed for nearly 20 years.
After Plato’s death in 347 BCE, Aristotle left Athens and spent time traveling and studying in Asia Minor and Lesbos. In 343 BCE, he was invited by King Philip II of Macedon to tutor his son, Alexander—who would later become known as Alexander the Great.
After tutoring Alexander, Aristotle returned to Athens and founded his own school, the Lyceum, in 336 BCE. There, he gathered a large group of students and began writing extensively. Aristotle’s works span a wide range of topics, including logic, ethics, politics, metaphysics, biology, and the arts, making him one of the most influential thinkers in history. He passed away in 322 BCE in Euboea.
Logic
Aristotle is often credited with founding formal logic. His work on syllogism laid the groundwork for deductive reasoning, which dominated Western thought for over two millennia. His Organon is a collection of texts that formed the core of logical theory.
Here’s a basic example of Aristotle’s syllogism in the form of categorical logic:
- Major Premise: All men are mortal.
- Minor Premise: Socrates is a man.
- Conclusion: Therefore, Socrates is mortal.
This is a valid syllogism because, given the premises, the conclusion logically follows.
Aristotle’s syllogisms are structured in a way that ensures the conclusion follows necessarily from the premises. The relationship between the terms in the syllogism is crucial. For example:
- Major Term: This is the predicate of the conclusion (the term that describes something in the conclusion).
- Minor Term: This is the subject of the conclusion (the term that is being described).
- Middle Term: This appears in both premises but not in the conclusion. It helps connect the major and minor terms.
In the example:
- Major Term: Mortal (predicate of the conclusion “Socrates is mortal”).
- Minor Term: Socrates (subject of the conclusion).
- Middle Term: Man (which connects the two premises).
Aristotle’s Three Laws of Logic:
Aristotle also contributed to the formulation of the basic principles of classical logic. These include:
- The Law of Identity:
- A is A (something is identical to itself).
- Example: If “A” is a dog, then it is a dog and cannot be anything else.
- The Law of Noncontradiction:
- Nothing can both be and not be (a statement cannot be both true and false at the same time in the same context).
- Example: It cannot be true that “Socrates is both mortal and immortal at the same time and in the same respect.”
- The Law of the Excluded Middle:
- Every statement is either true or false (there is no middle ground between truth and falsehood).
- Example: Either “Socrates is mortal” is true, or it is false—there’s no middle state.
Metaphysics
The word “metaphysics” appears to have been coined by the first century AD editor who assembled various small selections of Aristotle’s works to create the treatise we know by the name Metaphysics. Aristotle called it “first philosophy”, and distinguished it from mathematics and natural science (physics) as the contemplative philosophy which is “theological” and studies the divine.He wrote in his Metaphysics:
If there were no other independent things besides the composite natural ones, the study of nature would be the primary kind of knowledge; but if there is some motionless independent thing, the knowledge of this precedes it and is first philosophy, and it is universal in just this way, because it is first.
Epistemology
Aristotle’s immanent realism means his epistemology is based on the study of things that exist or happen in the world, and rises to knowledge of the universal, whereas for Plato epistemology begins with knowledge of universal Forms (or ideas) and descends to knowledge of particular imitations of these. Aristotle uses induction from examples alongside deduction, whereas Plato relies on deduction from a priori principles.
Physics
The Four Causes
Aristotle believed that to fully understand an object or event, you need to look at four types of causes:
- Material Cause: What is something made of? (e.g., the bronze of a statue)
- Formal Cause: What is its design or structure? (e.g., the shape of the statue)
- Efficient Cause: What brought it about? (e.g., the sculptor’s work)
- Final Cause: What is its purpose or goal? (e.g., the statue is made to honor someone)
For Aristotle, everything in the natural world can be explained by these four causes, and all things in nature are constantly striving to fulfill their final cause or purpose (a concept known as teleology).
The Four Elements
Aristotle believed that the entire physical world was made up of four elements:
- Earth (solid)
- Water (liquid)
- Air (gaseous)
- Fire (aether, or a “spiritual” element, in the celestial realm)
Each of these elements had certain natural tendencies:
- Earth and Water tend to move downward (towards the center of the universe), while
- Air and Fire tend to move upward (towards the outer reaches of the universe).
This theory of elements was central to Aristotle’s view of the cosmos, though it was eventually replaced by modern atomic theory.
The Concept of Motion and Change
Aristotle made a distinction between different kinds of motion and change:
- Locomotion: The movement of objects from one place to another.
- Alteration: A change in quality (e.g., a piece of wood becoming charred by fire).
- Growth and Decay: The process of increasing or decreasing in size (e.g., a plant growing or a body decomposing).
He believed that everything in the natural world was in a state of constant change (called becoming), but for any change to occur, something must cause it. This idea is part of his broader concept of motion, which he believed to be an inherent quality of nature.
Important Point: Aristotle rejected the idea of vacuum (empty space) and thought that everything in the universe was filled with some kind of substance. So, motion could only happen in a “medium” (air, water, etc.).
Natural vs. Violent Motion
According to Aristotle, there are two types of motion:
- Natural Motion: This is motion that occurs in accordance with the nature of the object (like a rock falling to the ground). For example, heavy objects naturally move toward the center of the Earth.
- Violent Motion: This is motion that is forced upon an object, going against its natural tendency (e.g., a thrown object). Aristotle believed that violent motion required a continuous force to keep an object moving.
This view of motion influenced scientific thought for many centuries, but was eventually replaced by Newton’s First Law of Motion, which states that an object in motion will stay in motion unless acted on by an outside force.
The Unmoved Mover
One of Aristotle’s most famous ideas was the Unmoved Mover. In his work Metaphysics, Aristotle argues that there must be something that causes all motion without itself being moved. This “first cause” or “prime mover” is eternal, immaterial, and perfect. It sets everything else in motion without itself being moved.
This idea had a major impact on later philosophy and theology, influencing thinkers like Thomas Aquinas, who associated the Unmoved Mover with God.
Astronomy
The Earth at the Center of the Universe
Aristotle believed in a geocentric model of the universe, meaning that the Earth was the center of the cosmos, and everything else (the Moon, Sun, planets, and stars) revolved around it. This model was later developed and formalized by Ptolemy in the 2nd century CE but was based on the thinking of philosophers like Aristotle.
In Aristotle’s view:
- The Earth was the center of the universe.
- The planets, the Sun, and the stars all moved in perfect, circular orbits around the Earth.
- This model suggested that everything in the universe was ordered and finite—there was a clear division between the imperfect, changing world below the Moon and the perfect, unchanging realm above the Moon.
The Celestial Realm vs. The Sublunary Realm
Aristotle made a distinction between two regions of the universe:
- The Sublunary Realm: Everything below the Moon. This realm was composed of the four classical elements: Earth, Water, Air, and Fire. It was subject to change and decay (birth, growth, death).
- The Celestial Realm: Everything above the Moon. This region was made of a fifth element, called aether (sometimes called “ether”), which was pure and unchanging. The stars, planets, and the heavens themselves were composed of this perfect substance.
Aristotle believed that celestial bodies were made of aether, unlike the earthly elements, which could undergo change and decay. In his cosmology, the heavens were eternal, unchanging, and perfect, while everything on Earth was subject to imperfection and change.
Classification of living things
Division into Plants and Animals
Aristotle divided all living organisms into two broad categories:
- Plants (Vegetable Kingdom)
- Animals (Animal Kingdom)
This simple division is still the foundation of the major taxonomic groups in modern biology (though the boundaries between kingdoms have evolved).
Classification of Animals
Aristotle was particularly interested in animals and how they could be categorized based on their characteristics. His animal classification system was based on several key criteria:
- Blooded vs. Bloodless Animals
Aristotle classified animals based on whether they had blood or not. He divided the animal kingdom into two main groups:- Blooded Animals (those that have red blood): This included mammals, birds, fish, amphibians, and reptiles.
- Bloodless Animals (those without red blood): This included insects, crustaceans, and other invertebrates like worms and mollusks.
- Air-breathing vs. Water-breathing
Aristotle made a further distinction between animals that breathe air and those that live in water:- Land animals (those that breathe air, such as mammals and birds)
- Aquatic animals (those that live in water, such as fish and amphibians)
- Vertebrates vs. Invertebrates
While Aristotle didn’t have the modern understanding of vertebrates and invertebrates, he was aware of the differences between animals with backbones (such as mammals, birds, and fish) and those without (like insects, mollusks, and other invertebrates). - Different Types of Animal Movement
Aristotle also categorized animals based on how they moved:- Walking animals (mammals, some birds)
- Flying animals (birds, insects)
- Swimming animals (fish, aquatic mammals like whales)
Classification of Plants
Aristotle’s classification of plants was much less sophisticated compared to his system for animals, but he did attempt to classify plants based on their structure and function:
- He identified herbs, shrubs, and trees as broad categories, noting their different growth habits.
- He observed that plants differed based on their lifespan and reproductive structures—whether they were annuals (live for one year), biennials (live for two years), or perennials (live for many years).
- However, unlike animals, Aristotle did not delve deeply into a detailed classification system for plants, leaving much of their study to be further developed by later naturalists.
Famous Quotes
- “We are what we repeatedly do. Excellence, then, is not an act, but a habit.”
- “Knowing yourself is the beginning of all wisdom.”
- “The whole is greater than the sum of its parts.”