David Hume’s Theory of Knowledge

Brief Background on Hume’s Theory of Knowledge

Hume’s theory of knowledge was very much influenced by both Newton’s scientific view of the world and John Locke’s theory of knowledge.

On the one hand, Hume appropriated Newton’s view of the universe in his philosophy. For Hume, following Newton, the universe has its own nature and dynamics which is intelligible by the human mind. What the human mind can hope for, therefore, is to simply describe how the universe works through systematization or the act of putting together the series of events into a single whole.

On the other hand, following Lock, Hume believes that all forms of knowledge come from experience. This explains why Hume rejects the rationalist position that there is a supersensible or transcendent source of knowledge. Yet, Hume’s conclusion is more skeptical than Locke’s. As is well known, Locke argues that knowledge is limited only to things that can be experienced. As a matter of fact, Locke says that reason has no room to operate when it comes to ideas that cannot be experienced, such as freedom and immortality of the soul. For Hume, we need to suspend our judgment when we delve into subjects remote from the affairs of common life and experience. Hume’s position is famously known as “moderate skepticism”.

Key Concepts of Hume’s Theory of Knowledge

On the Nature of Ideas. As Locke argues, ideas come from sensation and reflection. Hume calls it impression. Hence, when we say “impression” in Hume, this includes both sensation and reflection in Locke. And for Hume, ideas come from impression.

Following Locke, Hume claims that out of simple ideas the mind forms compound or complex ideas. For example, out of the simple ideas such as “horse” and “horn”, the mind can come up with a compound idea of a “unicorn”.

According to Hume, ideas that do not represent something in reality is an abstract idea and, therefore, meaningless. The idea of a “unicorn” is an example of an abstract idea because in the first place, there is no unicorn in reality.

Association of Ideas. According to Hume, there is a multiplicity of ideas, yet all these ideas are linked together forming a coherent whole. For Hume, this is made possible by the “laws of association”.

There are three laws of association according to Hume, namely: 

1) resemblance, 

2) contiguity in time or place, and 

3) cause and effect.

In the law of resemblance, Hume says that the idea of one object tends to call to mind ideas of resembling objects. For example, the idea of “man” resembles the ideas of “thinking”, “corporeal”, “mutable”, and “finite”.

In the law of contiguity in time and place, Hume says that when we think, for example, of “Hitler”, we tend to think of the “Holocaust”, “concentration camp”, and “Nazism”.

In the law of cause and effect, Hume says that when we think of, for example, the idea of a “fresh egg falling to the ground”, it calls to mind the idea of a “splattered mess”.

It is important to note that Hume puts more emphasis on the third law of cause and effect. In fact, the law of cause and effect is one of the most important concepts in Hume’s theory of knowledge. This explains why after talking about the law of cause and effect, Hume proceeds to the discussion on “perception” and “reasoning”.

Hume on Perception and Reasoning

Human understanding, according to Hume, is furnished with…

1) the faculty of perception and 

2) the faculty of reason. 

On the one hand, the object of perception are impressions or ideas. On the other hand, the object of reason are propositions.

According to Hume, propositions are either 

1) a priori statements about relations of ideas or 

2) empirical statements about matters of fact and real existence.

Relations of ideas, according to Hume, can be known intuitively or demonstratively. 

For example, the proposition “All triangles have three angles” is an example of a proposition that can be known intuitively.  

The proposition “The sum total of all three angles in a right triangle is equal to 180 degrees” is an example of a proposition that can be known demonstratively.

It is important to note that in relations of ideas, the truth can be established without empirical evidence. In fact, in both examples above, we don’t need to resort to experience before we can truly say that all triangles have three angles or, indeed, the sum total of all three angles in a right triangle is equal to 180 degrees. Through mental processes alone, we can truly say that indeed the propositions above are absolutely true.

Matters of fact, according to Hume, are propositions whose truth can be discovered through experience alone. Consider, for example, the proposition “Sugar is sweet”. Obviously, one cannot really say that indeed sugar is sweet if one has not tasted it. Hence, we can never come to know that sugar is sweet without resorting to experience.

It is must be noted that it is “matters of fact” that concerns Hume. In fact, Hume’s theory of knowledge centers on the idea of “matters of fact”.

Hume asks: “What is the nature of the empirical evidence which assures us of any real existence of matters of fact?”

According to Hume, we are assured of some facts by the present testimony of our senses or by the records of our memory. In other words, for Hume, we know that facts exist in reality simply because we experience them. This explains why Hume was an empiricist.

But the question is by what means do we get beyond such facts? In other words, how can we be sure that such facts exist in reality? This is the central question in Hume’s theory of knowledge, which he developed in his famous work Enquiry Concerning Human Understanding.

So, again, by what means do we get beyond such facts?

According to Hume, it is by means of the relation of cause and effect that we are enabled to make, more or less reasonable, predictions and conjectures that go beyond the data of perception and memory.

But how do we arrive at the knowledge of cause and effect?

The answer, for Hume, is not reasoning a priori (as the rationalists would have us believe) but entirely from experience. Again, for Hume, our knowledge of cause and effect relation remains limited to experience. Of course, the mind steps beyond experience and engage in reasoning. But for Hume, this kind of reasoning is not supported by any argument or process of understanding through relations of ideas or through reasoning a priori. This kind of reasoning, for Hume, is supported by habit or custom.

Now, it must be noted that for the rationalists, cause and effect relation falls under a priori reasoning. In other words, for the rationalists, there is a necessary connection between cause and effect. For example, if it is raining at the moment, then reason tells us that the road must be wet. However, for Hume, in reality there is no necessary connection between two events, between cause and effect. The idea of a necessary connection is produced in the mind not through reason a priori, but through habit or custom. Hence, Hume did not reject the idea of “connection” wholesale. He only rejects the idea of connection employed in metaphysical reasoning, that is, the a priori reasoning in rationalism.

Again, for Hume, there is (necessary) connection only through experience (in common life and practice) which is based on habit. 

Hence, the only evidence assuring us of any real existence and matters of fact is experience, that is, 

1) the present testimony of our senses, 

2) the records of our memory, and 

3) the causal (experiential) reasoning based on the empirically 

         observed regularities of past experience. As Hume writes:

“Knowledge of reality can only be derived from a careful observation of the ‘constant conjunction’ between contingent events. Where such constant conjunction is observed, we are inclined to attribute a causal relationship between events designated as ’cause and effect’.” See David West, An Introduction to Continental Philosophy (Cambridge, UK: Polity Press, 1986), p. 15.