In our last lesson, we navigated the elegant but austere universe of Baruch Spinoza, a single substance—Deus sive Natura—expressing itself through the parallel attributes of Thought and Extension. We saw how his radical monism offered a powerful, deterministic solution to the problems left by Cartesian dualism. Today, we turn to another of the 17th century's great rationalists, Gottfried Wilhelm Leibniz, who, faced with the same set of problems, constructed a metaphysical system that is in many ways the mirror image of Spinoza's.
Where Spinoza saw unity, Leibniz saw an infinite plurality. This lesson explores his ingenious and intricate response to Descartes: a universe composed not of one substance, but of an infinite number of them. Our learning goal is to explain Leibniz's celebrated and often misunderstood doctrine of monads—the fundamental, non-interacting building blocks of reality—and the pre-established harmony that orchestrates their existence. For a mind accustomed to building models from first principles, Leibniz's system offers a fascinating example of metaphysical engineering, starting from a critique of existing physics and deducing the nature of reality.
1. Beyond Extension: Substance as Force and Unity
Like Spinoza, Leibniz began with a deep dissatisfaction with Descartes's philosophy, particularly his definition of matter. For Descartes, the essence of corporeal substance was simply extension—the property of taking up space. Leibniz found this definition sterile and incomplete. How could something merely passive and divisible be the fundamental reality? A true substance, he argued, must be a source of activity; it must possess an intrinsic force.
Furthermore, anything that is extended is, by its very nature, divisible. You can always imagine cutting a piece of matter in half. For Leibniz, something that is infinitely divisible cannot be a true, fundamental unity. It is always an aggregate, a collection of other things. A true substance must be a genuine unum per se, a thing that is "one in itself."
Gottfried Wilhelm Leibniz - Stanford Encyclopedia of Philosophy
This article from the Stanford Encyclopedia of Philosophy (SEP) provides an authoritative overview of Leibniz's philosophy. We will start with his core conception of substance.
Please read the two subsections titled "Unity" and "Activity". Focus on these key points: Why Leibniz believes that "what is not truly one being is not truly one being either." His argument that anything divisible, like Cartesian matter, can only be an aggregate of substances, not a substance itself. His critique that the essence of substance must be activity or force, something that Cartesian extended matter lacks.
Leibniz’s critique leads to a radical conclusion. If substances must be active and indivisible unities, they cannot be physical in the way we normally think. They cannot be extended. This insight paves the way for his most famous metaphysical doctrine: the monad.
2. The Monads: True Atoms of Nature
Having rejected extended matter as the ultimate basis of reality, Leibniz posits that the world is fundamentally composed of an infinite number of simple, unextended, non-physical substances, which he calls monads (from the Greek monas, meaning "unit").
These are the "true atoms of nature," but unlike the physical atoms of Democritus or modern science, they are not tiny bits of matter. They are metaphysical points of force, activity, and—as we will see—perception. To grasp their nature, it is best to turn to Leibniz's own concise and definitive text on the subject, the Monadology.
Leibniz's Monadology - Marxists Internet Archive
This is the foundational text for Leibniz's late metaphysics. We will read the opening paragraphs where he lays out the essential properties of monads.
Please read paragraphs 1 through 13. Focus on understanding the following core characteristics: §1-3: Monads are simple substances, meaning they are without parts and therefore unextended and indivisible. §4-6: They cannot be formed or destroyed by natural means (composition or decomposition). They begin only by creation and end only by annihilation. §7: They are "windowless." Nothing can causally enter or leave a monad. They are completely self-contained. §8-9: They must have qualities and each one must be unique. This is an application of his Principle of the Identity of Indiscernibles—if two things were qualitatively identical, they would be the same one thing. §10-13: They are in a state of continuous change, which must arise from an internal principle.
These first few points present a startling picture of the universe. Reality is not a continuous whole (like Spinoza's substance) but a collection of an infinite number of discrete, causally isolated, soul-like entities.
3. The Inner Life of a Monad: Perception and Appetition
The "windowless" nature of monads raises a critical question: If nothing can cause a monad to change, how does change happen? Leibniz's answer is that the principle of change is entirely internal. Each monad has an inner life, which he describes using two key terms: perception and appetition.
- Perception: This is not necessarily conscious awareness. For Leibniz, perception is the internal state of a monad that represents the entire universe from its unique point of view. Every monad is a "living mirror of the universe," reflecting everything else, though most of these perceptions are "confused" or "minute" (unconscious).
- Appetition: This is the internal principle of change, the striving or tendency that drives the monad from one perception to the next. It is the internal "program" that unfolds the monad's entire history of states.
The following video lecture provides an excellent explanation of this internal dynamic and the hierarchy it creates.
A History of Philosophy | 39 Leibinz's "Monads"
In this lecture, the speaker from Wheaton College introduces the internal life of monads and the resulting hierarchy of being.
Please watch from the beginning to the explanation of appetition. Pay attention to the distinction between simple perception, sense perception in animals, and apperception—the self-conscious, reflective awareness that characterizes "spirit" monads (like human minds).
This leads to a hierarchy of monads, distinguished by the clarity of their perceptions:
- Bare Monads: Have only minute, unconscious perceptions. These constitute what we would call inanimate matter (like rocks or water).
- Souls: Have more distinct perceptions, accompanied by memory. These are the dominant monads in animals.
- Spirits: Have apperception—the capacity for reason, reflection, and knowledge of eternal truths. These are the dominant monads in human beings.
Leibniz's famous "mill" argument powerfully illustrates why perception cannot be a mechanical process.
Leibniz's Monadology - Marxists Internet Archive
Let's return to the Monadology to see Leibniz's argument against materialism.
Read paragraph 17, the "mill" argument. Notice the reasoning: if you could scale up a thinking machine and walk inside, you would only see parts pushing one another, never the thought or perception itself. Therefore, perception must belong to a simple, non-composite substance, not a machine.
4. The Solution: Pre-Established Harmony
We now arrive at the central challenge for Leibniz's system. If the universe consists of an infinite number of windowless monads, none of which causally interacts with any other, how do we explain the order and apparent interaction we observe everywhere? How is it that my mind's desire to raise my arm (an event in one monad) corresponds perfectly with the physical motion of my arm (events in an aggregate of other monads)?
Leibniz's solution is his doctrine of pre-established harmony.
Imagine two perfect clocks that always show the exact same time. How could this be?
- Mutual Influence: The mechanism of one clock could somehow influence the other (like Descartes' problematic mind-body interaction).
- Constant Intervention: A watchmaker could constantly adjust one of the clocks to keep it in sync with the other (this is the theory of Occasionalism, which Leibniz rejected).
- Initial Synchronization: A master watchmaker could have constructed both clocks with such perfection at the outset that they would remain in perfect sync forever, without any further interaction.
Leibniz argues for the third option. God, the supreme architect, created each monad with a pre-programmed "script" of perceptions that unfolds over time. He created all these monad-scripts in such a way that they are perfectly synchronized with every other monad's script.
The following video explains this solution clearly.
Dr. Darren Staloff, The Philosophy of G. W. Leibniz
This lecture by Dr. Darren Staloff uses the clock analogy to explain pre-established harmony.
Please watch the segment from explaining pre-established harmony. The lecturer correctly notes that for Leibniz, it's not just two clocks, but an innumerable number of clocks, all perfectly timed to each other.
Thus, the appearance of causality is just that—an appearance. When I will my arm to rise, the mental event (in my dominant monad) does not cause the physical event (in the monads that constitute my arm). Rather, God has harmonized them from the beginning, so that the will to act and the action itself occur in perfect, pre-established correspondence.
The SEP article provides a concise, step-by-step reconstruction of the argument for pre-established harmony, which will appeal to your preference for formal structure.
Gottfried Wilhelm Leibniz - Stanford Encyclopedia of Philosophy
This section presents the argument for pre-established harmony in a structured, five-step form.
Read the section titled "Pre-established Harmony," paying close attention to the five numbered points that lay out the argument. This shows how the doctrine follows from the denial of causal interaction and the nature of monads as spontaneous, self-contained entities.
5. Mind-Body Union and the Two Kingdoms
Pre-established harmony provides Leibniz's definitive solution to the mind-body problem. The mind (a spirit monad) and the body (a complex aggregate of subordinate monads) form a "union" not through causal influx, but through perfect, pre-ordained conformity.
Leibniz describes this as a harmony between two "kingdoms":
- The Kingdom of Nature, where bodies operate according to the laws of efficient causes (the laws of motion and physics).
- The Kingdom of Grace, where spirits operate according to the laws of final causes (purposes, goals, desires, and moral reasons).
These two realms do not interfere with each other, but they run in perfect parallel. God, as both the perfect Architect of nature and the just Monarch of spirits, has ensured that the two systems are harmonized.
Leibniz's Monadology - Marxists Internet Archive
Leibniz himself explains this harmony beautifully toward the end of his Monadology.
Please read paragraphs 78 through 89. Focus on how Leibniz describes the harmony between: The soul's laws (final causes) and the body's laws (efficient causes) (§78-79). His specific critique of Descartes for not knowing the full conservation laws of physics (§80). The broader harmony between the "physical realm of nature" and the "moral realm of grace" (§87-89), which ensures that, in the long run, the physical world serves the moral purposes of the spiritual world (e.g., rewards and punishments).
Conclusion
Leibniz presents a universe of staggering complexity and ingenuity. In response to Descartes, he banishes causal interaction between substances altogether. Instead of Spinoza's single, all-encompassing substance, he populates reality with an infinity of individual, soul-like monads. The order of this pluralistic universe is not maintained by interaction or identity, but by a divine, pre-established harmony that synchronizes the inner life of every substance.
Key Takeaways:
- Monads as Substance: True substances are simple, indivisible, unextended, and active entities called monads. They are "windowless" and do not causally interact.
- Perception and Appetition: Each monad has an internal life, consisting of perceptions (representations of the universe from a unique viewpoint) and appetition (the internal drive for change).
- Hierarchy of Monads: Monads differ in the clarity of their perceptions, forming a hierarchy from bare monads (matter) to souls (animals) and spirits (humans).
- Pre-Established Harmony: The apparent interaction and order in the universe are the result of a divinely pre-ordained synchronization of all monads, which unfold their internal states in perfect concert, like an infinite number of perfectly made clocks.
- Mind-Body Solution: The mind and body are not causally linked but are harmonized. The soul follows the laws of final causes (purposes), while the body follows the laws of efficient causes (physics), and their states correspond perfectly.
Preview of the Next Lesson:
Our exploration of Leibniz is not yet complete. The doctrine of pre-established harmony relies on the idea of a perfect God choosing to create the best possible arrangement. This choice is governed by another of Leibniz's great contributions to metaphysics: the Principle of Sufficient Reason. In our next lesson, we will examine this principle and its profound implications, including his famous and controversial claim that this is, indeed, "the best of all possible worlds."