David Hume’s Philosophy: Empiricism, Knowledge, and Causality
Hume’s Empiricism: Impressions, Ideas, and Knowledge Limits
Are there impressions derived from ideas? Yes. The impressions of reflection may follow their respective ideas, but only after the feeling and the ideas derived from them. Ideas of sensation, however, are derived from their corresponding impressions of sensation. Therefore, all the contents of the mind are rooted in sensory experience. (Treatise, Part One, Section Two).
Hume’s Knife: Meaning and Metaphysics
What is meant by Hume’s Knife? It is a methodological principle – reminiscent of that employed by William of Ockham – which states that if an idea cannot be reduced to its simplest constituents (impressions), the term designating that idea has no meaning. This criterion was used by Hume to challenge metaphysical speculations. We encounter something similar when studying the criteria of demarcation and meaning in logical positivism.
With this approach, Hume introduced a sharp criterion for deciding the truth of our ideas. Do we want to know if any idea is true? It’s very simple: we check whether this idea originates from some impression. If we can trace it back to the appropriate impression, we are dealing with a genuine idea; otherwise, we are dealing with a fiction. The limit of our knowledge is, therefore, impressions. He shares this fundamental premise of empiricism – that experience is the source of all knowledge – with Locke and Berkeley, but unlike them, Hume establishes that experience is also its limit.
Comparison with Logical Positivism and Popper:
- Neopositivists identified their criterion of demarcation (verifiability for some, falsifiability for others) between science and metaphysics with the criterion of meaning. Following Hume, they considered metaphysical propositions meaningless.
- Popper, however, distinguished his criterion of demarcation (falsifiability) between science and metaphysics from the criterion of meaning. For Popper, metaphysical propositions are not scientific but still possess meaning and play an important role in the discovery context of scientific theories.
Hume’s Microscope: Analyzing Ideas
What is meant by Hume’s Microscope? The famous “microscope” of Hume is a methodological principle for reducing a complex idea to its simple constituents: the impressions from which such an idea derives.
Hume’s Fork: Types of Knowledge
What does Hume’s Fork refer to? It is a methodological principle employed by Hume which leads him to establish the existence of two distinct types of knowledge:
- Knowledge of relations of ideas (e.g., mathematics, logic)
- Knowledge of matters of fact (e.g., empirical observations)
Hume’s View on Physics
According to Hume, Physics would not be the science of an unknown and unknowable external reality, whose existence we cannot even affirm. Instead, it is the science that examines the relationships between perceived events. It allows us to predict certain future events based on past observations, although without absolute certainty. For example, we expect that the Sun will rise tomorrow, that an object thrown into a fire will be consumed, or that falling into water without swimming will lead to drowning, etc.
The Problem of Causality
Why can we not accept that it is probably true that causal relationships exist? The causal relationship is not knowledge gained by the mind relating ideas; it is knowledge of matters of fact and is entirely dependent on experience. Therefore, we cannot sustain that it is *probably* true that causal relationships exist.
Why not?
- If we believe this statement represents necessary knowledge, experience cannot provide necessary truths.
- If we consider it probable knowledge attained from a series of experiences, this probability itself must be founded on a prior conviction of the probable existence of causal relationships (or the uniformity of nature).
This reasoning leads to an infinite regress (regressus ad infinitum). We assume the principle of causality (or uniformity) to justify knowledge from experience, but that assumption itself would need justification from prior experience, which requires the same assumption, and so on.