Hume on Our Supposed Knowledge of Causation
By Dr. Jan Garrett This is based on David Hume's Essay on Human Understanding. It is intended only for review purposes for students in Introduction to Philosophy at Western Kentucky University. This page revised November 18, 2009
* * * * Hume's general term for the particular contents of the mind is perceptions.
He divides them into what two classes, impressions and ideas.
He distinguishes them as follows: Impressions are more forcible and lively than ideas. The strongest idea is less forceful than the weakest impression.
Note that all perceptions are particular contents of the mind, e.g., we have perceptions of this red item or that sour item, not of redness as such. (Hume does not allow that there are abstract or general ideas, but there are general words or terms like "redness" or "humanity." Such words refer to what particular red things or human beings seem to have in common.)
We can acquire the (compound) idea of a golden mountain in spite of the fact that we have never seen one. The mind has the power to compound our simple ideas based directly upon impressions, so that we can create the co-occurrence of the ideas of gold and mountain even though we've never had an impression of gold and mountain together.
According to Hume, is the relationship between the ideas we actually have and impressions is very important.
All our ideas are nothing but copies of our impressions; it is impossible for us to think of any particular (simple) perception that we have not previously felt by our external or internal senses.
(External senses give us impressions of color, taste, sound, smell, etc.; internal sense gives us impressions of love, hate, anger, fear, etc.)
This is an empiricist position. All our knowledge is derived from sensation, either "external" or "internal."
If we suspect that a philosophical term is being used without any meaning— Hume uses "meaning" interchangeably with "idea"—we need only to inquire from what impression is that supposed idea derived. If we cannot find any such impression, this will serve to confirm our suspicion that the corresponding term (word or phrase) has no meaning.
Causality seems to be important in everyday life as well as in science and philosophy. Hume tries to prove that common words referring to causality are meaningless.
Our common notion of causality is compound, according to Hume. Upon close inspection, it turns out to consist of three parts, or two parts and words for a third. Causal events are supposed to be related to their effects as follows: (1) the causal event regularly precedes the effect event, (2) the causal event and effect event regularly occur in close proximity to one another (they are "contiguous"), (3) the causal event is necessarily connected to the effect event.
Hume focuses upon the alleged third component of the compound idea of causality, the "idea" of necessary connection, of power or force.
Something seems to be missing when we pay very close attention to what seem to be clear cases of causation, for instance, one billiard ball impacting a second and the second moving away in a predictable direction. We have no impression (direct perception) of a necessary connection between the events.
What we actually observe in such cases is this: The one type of event (the alleged effect) actually follows the other type of event (the alleged cause), over and over again, so far without exception.
For Hume the source of the feeling that when one object strikes another there is some force that "makes" the second move is no concrete perception or impression of force or necessary connection, but habit. Habit is not a feature of the external world (as causality is supposed to be) but a quality of persons having experience.
This feeling of causality is created in us as follows: When we repeatedly see one type of event followed by an event of another kind, we become habituated to the pattern and begin to expect that events of the first kind will always be followed by events of the second kind. There is nothing more to the so-called idea of causality than this habituated feeling.
If Hume is right, we can conclude about the claim that there is causality in the (external) events themselves that the claim is without meaning.
Nor do we have any good reason for thinking that future events will follow one another in a certain pattern because they have done so in the past. The reasoning that "because events of type A have always in the past been followed by events of type B, events of type A in the future will always be followed by events of type B" is fallacious. This reasoning commits the fallacy of circular reasoning. The only reason we expect the future sequence of events to be like past sequences is that, in the past, sequences in the future relative to that past moment were like past (i.e., earlier) sequences relative to the same moment.
All this implies that causation is nothing but an expectation in our minds, but even that expectation is logically unjustified.