Rationalism and Empiricism: Philosophical Knowledge Origins

Rationalism: The Primacy of Reason

René Descartes is widely considered the father of rationalism. Other prominent followers of this doctrine include Baruch Spinoza and Gottfried Wilhelm Leibniz.

Rationalism posits the following key theses:

1. Geometry as the Model of Knowledge

   Geometry serves as the authentic model of knowledge. From a few axioms, and using deductive reasoning and logical laws, a set of theorems can be derived. For rationalist philosophers, all knowledge must follow this rigorous model.

2. Distrust of Sensory Information

   Rationalism distrusts information about the world obtained through the senses. By contrast, the successes of geometry demonstrate that deductive reasoning can establish and expand knowledge reliably.

   For Descartes, the senses are unable to reveal reality as it truly is. He famously used the example of a piece of wax: when looking at or touching the material, sight and touch perceive colors and textures. However, when the wax is placed near fire, its texture and colors disappear, indicating that these were qualities not inherent to its true nature. Yet, one fundamental aspect remains unchanged: its extension – the fact of occupying space and having length, width, and depth.

   Mathematics thus becomes a science that allows escape from the deceptions of the senses to know reality as it is.

3. The Existence of Innate Ideas

   There are ideas in our minds that are innate. All human beings are born with these ideas, and therefore, they do not result from knowledge of the outside world. For example, the idea of infinity or the idea of God are concepts that cannot be derived from sensory information.

   This conception, as Descartes argued, was widely criticized because it would imply a baby should possess clear and evident ideas at birth. Leibniz attempted to explain this problem: innate ideas are indeed present in our minds at birth, but they must be developed throughout life, and through experience, to reach their full adult form.

Empiricism: Knowledge from Experience

Empiricists argue for radically different positions regarding the origin of knowledge. Key aspects that differentiate empiricism include:

• Knowledge Based on External Experience

  For empiricism, knowledge is based on external experience and is obtained through perception. They liken the mind to a blank slate (tabula rasa) that is filled with information received through the senses.

• Rejection of Innate Ideas

  Following the thesis that all ideas arise from experience and perception, empiricists conclude that there can be no innate ideas. One of the great challenges of empiricism is to explain the formation of complex ideas solely from sensory input.

The three most influential modern empiricist thinkers were John Locke, George Berkeley, and David Hume.

David Hume and the Rise of Skepticism

David Hume represents the culmination of empiricism. He applied its principles rigorously, which ultimately led him to skepticism. The classic ideas of rationalist metaphysics – such as the existence of the soul, divinity, and the external world – were the main targets of his criticism.

Hume's arguments are related to his proof that the principle of causality (the basis of all sciences until then) is not provable either through reason or through the senses. Science and metaphysics are, therefore, based on unproven assumptions.