Context

The author has been attempting to discover the nature of the philosophical relation of causation, which concerns objects that are not perceived by the senses. In Section 2, he had discovered that a component part of the relation is necessary connection. He was unable to find a basis for that relation when he considered it directly and so tried an indirect approach. The first question, examined in Section 3, was why we think that a cause is always required in the case of any beginning of existence. The answer was that our belief in the need for causes comes from experience. But rather than try to show straightaway how experience gives rise to the belief in a cause, the author first considers why we think that particular effects necessarily have their causes, as well as how we make inferences from effect to cause. The present section begins the latter investigation.

Background

Aristotle had argued in Book I, Chapter 3 of the Posterior Analytics that all inference must ultimately terminate in premises that are not the conclusions of other premises. Locke, in Book IV, Chapter 2 of the Essay, had held that conclusions of demonstrations must be based on intuitive premises which compare ideas [what the author calls “perceptions”]. But he did not consider the specific case of causal reasoning in this respect.

The Treatise

1. Any causal reasoning, either from effect to cause or from cause to effect, requires a starting-point in some actual perception, some mixture of impressions and/or ideas of memory, “which are equivalent to the impressions” [for this purpose, apparently]. The author discusses the inference from cause to effect to support this claim. If we are to establish the existence of an effect from the existence of a cause, the existence of the cause must itself be established. This can be done through perception or through the establishment of the existence of the cause of the cause. But this procedure cannot progress to infinity. [The author had argued against the infinite divisibility of ideas on the grounds of the finitude of the mind in Book I, Part II, Section 1, paragraph 2. The mind’s finite capacities are presumably the basis for the claim that causal reasoning cannot proceed to infinity.] Instead, we must eventually “arrive at some object, which we see or remember.” The impressions of sense and ideas of memory are the only things that can serve to prevent a regress, so all reasoning from causes to effects terminates with perceptions. Without a fixed stopping point in perceptions, “there wou’d be no belief nor evidence.”

2. To illustrate his case, the author gives an example of reasoning about the reality of historical events. As we do not observe them directly, we may either believe or disbelieve that they have occurred. The specific example is the death of Julius Caesar on the ides of March [March 15]. The common way of establishing the reality is by way of the fact that historians have testified unanimously that it happened. The author now describes the mechanism by which the fact is supposed to be established. We begin with an effect of a cause: “certain characters and letters present either to our memory or our senses.” These are present when we read a book of history. We take the cause of this written material to be ideas in the minds of the writers, and these ideas are effects of the perceptions of the writers themselves. Either they immediately witnessed the events, or they received their own perceptions in the manner just described, the chain eventually terminating with those who observed the event directly, “by a visible gradation.” But this “chain of argument” could not begin without the original perceptions of the characters and letters, seen or remembered. In their absence, “our whole reasoning wou’d be chimerical and without foundation.” There would be a chain with nothing to hang it upon. Hypothetical arguments [those which merely assume, and do not establish, their premises,] are in fact lacking in belief and evidence, “there being in them, neither any present impression, nor belief of a real existence.”

3. We need not be able to call up the original impressions [or ideas]: the memory of the conviction they have produced is enough even if “these impressions shou’d be entirely effac’d from the memory.” Causal reasoning proceeds in the same way as a demonstration based on comparison of ideas [such as in a mathematical proof], which “may continue after the comparison is forgot.”

The Enquiry

Hume does not explicitly treat this topic in the Enquiry. However, many of his examples of causal reasoning, especially in Section 4, take experience as the starting point of causal reasoning. The experience is generally described in terms of the presentation of an object, rather than the having of a perception. For example, “Were any object presented to us, and were we required to pronounce concerning the effect, which will result from it, without consulting past observations; after what manner, I beseech you, must the mind proceed in this operation?” (Section 4, paragraph 9).

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