Epistemology: Descartes, Leibniz, and Hume on Knowledge
The Problem of Knowledge and Rules of Method
The various sciences are simply different manifestations of a single find. This knowledge, the product of reason alone, can explain reality. Philosophy supports all sciences, “like a tree whose roots are metaphysics, the trunk physics, and the branches are all other sciences.” Descartes aims to find the true foundation of all knowledge and establish a universally valid philosophy. Many theories exist, but none has received universal acceptance, hence the need to develop a new philosophy. The failure of previous philosophers is due to the lack of an appropriate method. Mathematical science serves as a model: a precise, rigorous science with universal value, showing continued progress. The mathematical method should guide the building of philosophical knowledge that is precise and universally valid. This method relies on two mental operations: intuition, perceiving obvious and immediate axioms, and deduction, deriving new propositions (theorems) logically from premises. Using a set of rules until a conclusion is reached, we can move to other evident truths. Inspired by mathematics, Descartes proposes four methodological rules: evidence, analysis, synthesis, and counting. First, admit as true only what is known with evidence, understanding clearly and distinctly what is presented to the mind, beyond doubt. Second, divide each difficulty into as many parts as possible. Third, guide thoughts from the simplest objects to the complex. And finally, do thorough counts and comprehensive overhauls.
The Doubt, the Cogito, and the Criterion of Certainty
Descartes seeks a clear and absolutely true principle, the foundation of all knowledge, an axiom for a rigorous philosophical system. The method is methodical doubt, rejecting any idea with the slightest doubt. Theoretical doubt does not affect action, and new methods offer a more solid foundation. First, we doubt sensory knowledge, as senses can deceive. We must dispense with them as a reliable source of certain knowledge. The existence of an external world of real objects that strike our senses seems certain, but we doubt it due to the impossibility of distinguishing between wakefulness and sleep. Mathematical truths remain, but Descartes questions them: an evil genius or deceiving God could induce illusions. All our knowledge is subject to doubt until Descartes discovers the first evident truth: “cogito, ergo sum” (I think, therefore I am). My existence as a thinking subject is beyond doubt due to total evidence, appearing with absolute clarity and distinction. An idea is clear when “present and manifest to an attentive mind” and distinct when it cannot be confused with any other. This is the criterion of certainty: accept as true what is received clearly and distinctly. Can this be applied to other ideas? Descartes, perhaps trapped in solipsism, cannot ensure the existence of any fact except his own. From the cogito, all else follows. The first step is to prove that God exists and does not deceive us.
Metaphysics of Leibniz (Monads and Harmony)
Leibniz defends a pluralistic and dynamic conception of reality. Reality is constituted by an infinity of monads, indivisible and unextended elementary units, like atoms of energy or metaphysical points. Energy, an internal force or capacity for action, defines each monad. Monads are ingenerable and indestructible, created by God and annihilated only by God. Every real thing is an aggregate of monads. Inorganic beings are formed by the juxtaposition of monads. Organic beings have an external governing monad, the “soul,” grouping the others. Monads have two characteristics: perception, the ability to represent something external, and appetition, the internal force or tendency to change. Each monad is a microcosm, a reflection of the entire universe. In humans, perception becomes conscious in the “understanding,” and appetition is free, the “will.” Monads are closed units, yet there appear to be influences between them, especially in the soul-body interaction. Leibniz explains this with pre-established harmony: God has perfectly synchronized the activities of soul and body. Leibniz defends cosmic optimism: we are in the best possible world. God is guided by the principle of perfection, a sufficient reason for creation. Evil is a necessary condition for the system to work.
Types of Knowledge in Leibniz and Hume
LEIBNIZ | HUME | |
1st Truth or knowledge | “Truths of reason: Inborn, discovered as true independently of experience (a priori). Necessary: they cannot be otherwise. Principle of contradiction: something cannot be both itself and its opposite. Analytic: the predicate is already contained in the subject. | Relations between ideas: No need to resort to experience. Verification is a priori, necessary, and analytic, providing no new information because the predicate is implicit in the subject. They are based on the principle of contradiction: the opposite is impossible. This type of knowledge belongs to formal sciences. |
2nd truth or knowledge | “Truths of fact: Acquired: From experience (a posteriori). Contingent: they may be one way or another or not be. Principle of sufficient reason: everything that happens has a reason for its existence. Synthetic: the predicate extends the notion of the subject. | Matters of fact: Knowledge characteristic of experimental science. Propositions describing facts, their validity depends on a posteriori (empirical) evidence. They originate in impressions. The opposite of a matter of fact involves no contradiction. All knowledge of facts is based on the principle of causality. |