David Hume: Theory of Knowledge and Metaphysics
The Nature of Ideas and Memory
Ideas: The memory of the object is given by absent impressions and is presented as the second item of knowledge. They are weaker than impressions and can be divided into simple and compound. Just as simple impressions give rise to simple ideas, a composite impression gives rise to a composite idea. Also, we can relate ideas, resulting in a composite idea for which we do not have a direct impression; therefore, it is not true (relation of ideas).
Direct Perception and Impressions
Impressions: This is the direct perception we have, which includes sensations, passions, desires, and emotions present in the moment. For example, considering a color or feeling hate refers to impressions, enabling us to classify them into:
- Impressions of sensation
- Impressions of reflection
The Concept of Cause and Effect
The Idea of Cause: For Hume, reason is a necessary notion in his work. An object (the cause) is followed by another when all objects similar to the first are followed by objects similar to the second. This second object is meant as the effect. As we have no impression of a necessary connection between cause and effect, the only reliable way to say something is a cause is when the effect has been given in the presence of what you consider the cause.
Understanding Relations of Ideas
Relations of Ideas: Relations of ideas are a kind of knowledge that can be said to be true or real because this truth or certainty is independent of experience. That is to say, they do not refer to facts which we assume through experience, but we establish relations between different ideas. Thus, the validity of the ideas comes from the connection between themselves. This is the kind of knowledge found in basic formal logic and mathematics.
The Phenomenon and Sensory Reality
Phenomenon: Given that our knowledge allows us to go no further than impressions or sensible data, what experience or reality is for us is nothing but a series of appearances. This is what is shown, but I suppose we stand firm in the belief that behind what is shown, there is something hidden that is not displayed and causes what appears—something that has generated an impression in our sensory organs.
Metaphysics and the Limits of Human Knowledge
Metaphysics: A portion of philosophy in charge of studying "being." For Hume, true philosophy signifies deep and abstract reflection on the complexity of human nature, specifically regarding the capacity for knowledge—building the capacities and limits of human knowledge. It is from metaphysics or philosophy that we could help validate science, showing how and toward where it can orient its research. Hume’s thesis is that human knowledge is not unlimited; he denies the metaphysical understanding of meta-empirical realities (those beyond experience) such as God and the soul. He considers dogmatic metaphysics to lead inevitably to superstition.