David Hume’s Theory of Knowledge: Impressions and Ideas
Theory of Knowledge: Hume’s Insights
Hume believed that all sciences have a more or less large connection with human nature: the “science of man” is the only solid foundation for other sciences. We, therefore, investigate the nature of human understanding to learn about its capabilities.
The Origin of Ideas
David Hume did not agree with the dogmatism of Descartes. His position was essentially critical of rationalism, although he accepted the fundamental immanentist postulate: the subject never fails to pass the field of mental representations because the human mind does not grasp any other goal than its ideas. Both for Hume and Descartes, ideas are non-intentional, i.e., they do not refer to reality. We are not allowed to see reality because the only thing we can know are ideas.
The difference between the thought of Hume and Descartes is not in what they both mean by “idea,” but in the root of it. According to rationalism, the human mind is a trunk where all ideas reside; that is, there are innate ideas. According to empiricism, the mind is a machine that makes ideas. The idea is not waiting for me to intuit, but I am the one who makes it. For this reason, for empiricists, the psychological process of the formation of ideas is very important. Therefore, the essential question of empiricism is: How can we come to have ideas? Rationalism is, then, for Hume, dogmatic, as it does not ask this fundamental question.
To answer the essential question of empiricism, Hume began by denying innate ideas. Against the Cartesian approach, the empiricist begins to assert, as Aristotle had done, that all knowledge comes from experience. Having established this, we only have to see what process is followed for the formation of ideas.
Hume derives all contents of the mind from experience. All knowledge comes down to perception, perception being understood as everything the spirit contains. Perceptions are divided into impressions and ideas. Impressions are the external sensations, such as images of external objects, and internal sensations, passions, and emotions. Ideas are blurred images of impressions. Let’s see if this is seen more clearly with an example: If you look at an object and then close your eyes, trying to imagine this object, when you look and when you imagine, you are perceiving (or knowing), but between them, there is a remarkable difference. The perception of the object is more alive when we see it than when we imagine it. The first is what Hume called impressions (consciousness through the senses), and the second, ideas (representations or copies of impressions in thought). Ideas are weaker, less vivid than impressions. The example we used also makes it clear that ideas come from impressions; they are images or representations of them.
At first, he says, then, that ideas and impressions always correspond to each other. But this must be qualified. He draws a distinction between simple and complex perceptions. Therefore, there are simple and complex impressions and simple and complex ideas. Simple perceptions, whether impressions or ideas, are those that do not support distinction or separation. Compound perceptions, both impressions and ideas, are those that allow separated parts. For example, the perception of a red spot is a simple impression, and the thought (or image) of it is a simple idea. But if I go to the castle of Bellver and see from there the city of Palma, I get a complex impression of the city (of roofs, chimneys, etc.), and when I then remember this impression of Palma, I have a complex idea.
But there are also cases in which a complex idea does not correspond to any complex impression, as might be the idea that I can have of a city where the pavement is made of gold and the walls of rubies. Therefore, strictly speaking, we cannot say that every idea corresponds to an impression. But we should note that a complex idea, such as the one mentioned above, can be decomposed into simple ideas. Then we can ask whether every simple idea corresponds to a simple impression, to which Hume responds affirmatively.
Having said that, we can say that the origin of ideas is empirical; all simple ideas are derived from simple impressions.
But ideas are not disconnected in the mind. Imagination is not entirely free in the task of forming ideas but is governed by the laws of association, which, as a gentle force, ensure that ideas are not unconnected and unrelated. The imagination is governed, then, by three laws:
- The law of similarity, which tends to unite similar things; for example, thinking of a portrait suggests the person depicted.
- The law of spatial and temporal contiguity, which tends to unite things that are contiguous in space and time; for example, seeing the Colosseum leads to thinking of Rome.
- The law of cause and effect: the observation of smoke makes us think of fire.
One might wonder, then, after all this, what happens with general ideas. Hume is very clear, and his position on this is why we can say he is a nominalist. Hume denies general ideas, saying that, properly speaking, there are no general and abstract ideas, but that all general ideas are really just particular ideas related to a general term that recalls other individual ideas that are similar in certain details to the idea in the mind. In other words, it’s only just a name (hence the term nominalism) that encompasses a range of experiences that are only of something special.