Hume’s Philosophy: Empiricism and Knowledge
Hume’s Knife: A Principle of Simplicity
Hume’s Knife, a methodological principle reminiscent of Occam’s Razor (attributed to William of Ockham), asserts that if an idea cannot be reduced to its simplest components, the term designating that idea is meaningless. Hume used this criterion to dismiss metaphysical speculations. This concept is similar to the criterion of demarcation and meaning in logical positivism.
Hume’s approach introduces a strict criterion for determining the truth of ideas. To determine if an idea is true, we check if it originates from an impression. If a corresponding impression can be identified, the idea is real; otherwise, it is a fiction. Therefore, the limit of our knowledge is defined by impressions. This shares the fundamental premise of empiricism with Locke and Berkeley—that experience is the source of all knowledge—but, unlike them, Hume establishes experience as its *limit*.
Hume vs. Logical Positivism and Popper
Neopositivists (logical positivists) used the criterion of demarcation—verifiability for some, falsifiability for others—to distinguish between the scientific and the metaphysical, and this criterion also served as the criterion of significance. Following Hume, neopositivists considered metaphysical propositions to be meaningless. However, for Popper, the criterion of demarcation (falsifiability) between science and metaphysics does *not* coincide with the criterion of significance. Metaphysical propositions are not scientific, but they possess meaning and play a crucial role in the context of discovering scientific theories.
Hume’s Definition of Physics
According to Hume, physics is not the science of an unknown and unknowable external reality (whose existence we cannot definitively affirm). Instead, it examines the relationships between perceived events. We often anticipate certain facts or future events for which we have no current impressions. For example, we are certain that the sun will rise tomorrow, that an object thrown into a fire will burn, or that someone who cannot swim will drown if they jump into water.
Types of Knowledge According to Hume
1. Relations of Ideas
This category includes all propositions of geometry, algebra, and arithmetic. Statements like “the whole is greater than the parts” or “the sum of two and two equals four” express only the relationships between ideas (e.g., the relationship between ‘whole’ and ‘part’ in the first statement). These propositions can be derived through the operation of the mind, by reasoning alone, without needing experience. The truth of these propositions is independent of empirical verification.
These propositions represent the domain of certain knowledge because their opposites are impossible and imply a contradiction. They are *necessary truths*: what they state is firmly established and cannot be otherwise, based on the principle of non-contradiction. They are *analytic truths* because the predicate is contained within the subject and necessarily belongs to it. They are *true explanations* because they do not expand our knowledge but make it explicit, and they are true *a priori*, independent of experience. In the fields of logic and mathematics, absolute certainty can be achieved.
2. Matters of Fact
Knowledge that refers to facts depends entirely on experience. Statements like “gold is yellow” cannot be reached through simple argument; observation and experience are necessary. Truths of fact—the object of study of physics—are *synthetic*: the predicate is *not* contained within the subject. They are *contingent*, as what they state could be otherwise; their opposites do not involve a contradiction. They are *ampliative*: the knowledge they provide is greater than what was previously possessed. And they are *a posteriori* because they are established from experience and depend on it.
The only guarantee of the truth of propositions asserting facts is experience. Therefore, we can only be sure of what is present to the senses or registered in memory, but not of what transcends these boundaries. The opposite of every event is always possible; it implies no contradiction.