Notes on Hume’s Treatise

by G. J. Mattey

Book 1
Of the UNDERSTANDING
PART 4
Of the sceptical and other systems of philosophy.

Sect. 1. Of scepticism with regard to reason.

1. The rules in demonstrative sciences are infallible, but their application is uncertain. We must form a second judgment, a control, and keep track of our accuracy over time. Reason is a cause whose effects may be truth or not, so our tracking generates probabilities, which are “greater or less, according to our experience of the veracity or deceitfulness of our understanding, and according to the simplicity or intricacy of the question.”

2. Mathematics is an example: we double-check, ask our peers, see the response to publication. All this leads to a gradual increase in assurance. What accounts for this increase is “the addition of new probabilities, and this is deriv’d from the constant union of causes and effects, according to past experience and observation.” [See 1.3.12, “Of the probability of causes.” Based on what is said in paragraph 2, a “new probability” would be a greater degree of force in the habit which is built up by constant conjunction.]

3. In accounting, cross-checks are built into the process because the result of adding long strings of numbers could be nothing more than probability. The author goes on to propose a problem for all mathematical reasoning. As calculations become simpler and simpler, where does probability end and knowledge begin. We want to say that at the limit, in a single simple calculation, there is knowledge. But knowledge and probability are contrary, because “they will not divide, but each must be entirely present, or entirely absent.” Even the simplest addition, then, falls short of knowledge, since if it were knowledge, then a total sum would be, “unless the whole can be different from all its parts.” This is a classic version of the “sorites” or “heap” paradox.

4. The conclusion is that all of what is called “knowledge” is really probability, so that mathematical and other apparently certain forms of reasoning are nothing more than a species of ordinary probable reasoning. So the next question concerns the foundation of probable reasoning.

5. Just as reason requires correction, judgments of probability are subject “to a new correction by a reflex act of the mind, wherein the nature of our understanding, and our reasoning from the first probability become our objects.” The “first probability” here is the one which arises naturally based on constant conjunction, as described in Sections 11-13. The second arises from the evaluation of this first-order probability, taking into account our judgment and experience. Even the wisest person does not have complete confidence in his first-order probability judgments.

6. We have, now, the uncertainty of the original judgment and the uncertainty that is based on our observation of the weakness of the faculties. And there is a third, “deriv’d from the possibility of error in the estimation we make of the truth and fidelity of our faculties.” A regress then diminishes the original probability to “at last a total extinction of belief and evidence.” Whatever is finite (and the original probability is a finite strength of habit) is destroyed by infinite diminution. So no matter how strong the original probability, it is eventually worn down to nothing.

7. It would appear that anyone who accepts this argument would have to be called a skeptic, holding that everything is uncertain, and the author has presented the argument vigorously. Does the author hold that our judgment allows no measure of truth or falsehood? He does not, nor does anyone else, because they cannot. “Nature, by an absolute and uncontroulable necessity has determin’d us to judge as well as to breathe and feel.” By the same token, we cannot avoid the strength of habit (“viewing certain objects in a stronger and fuller light”) instilled by constant conjunction. “Whoever has taken the pains to refute the cavils of this total scepticism, has really disputed without an antagonist, and endeavour’d by arguments to establish a faculty, which nature has antecedently implanted in the mind, and render’d unavoidable.”

8. The role of the argument used by the “fantastic sect” of skeptics, then, is to confirm the account of causal reasoning (as the result of custom) and of belief (as an act of the sensitive rather than rational faculty). If belief “were a simple act of thought, without any peculiar manner of conception, or the addition of a force and vivacity, it must infallibly destroy itself, and in every case terminate in a total suspense of judgment.“ The fact that beliefs cannot be destroyed by “mere ideas and reflections.” confirms that it is “some sensation or peculiar manner of conception.”

9. The author recognizes that the skeptical argument can be applied to his own account of belief, however. The original probability is a belief of a certain strength. Reflection on one’s past judgments diminish the original belief some, and so on. “’Tis therefore demanded, How it happens, that even after all we retain a degree of belief, which is sufficient for our purpose, either in philosophy or in common life?”

10. The answer is that after the uncertainty of the object and the fallibility of the senses are considered, we move up to levels that are further removed from the original reasoning. The “forces of judgment” are the same at the higher levels, “yet their influence on the imagination, and the vigour they add to, or diminish from the thought, is by no means equal.” The higher-order reflection is “forc’d and unnatural,” resulting in “faint and obscure ideas,” “The attention is on the stretch: The posture of the mind is uneasy; and the spirits being diverted from their natural course, are not govern’d in their movements by the same laws, at least not to the same degree, as when they flow in their usual channel.”

11. The current treatise on metaphysics is an example. We scrutinize the arguments much more intensely than in ordinary life, and an argument that would be considered convincing in history or politics is not so in metaphysics. The explanation is that our thought is strained, disturbing “the operation of our sentiments, on which belief depends.” This is true in general. An example is that of a witty hero in tragic poetry: our passions would not be moved by such a one. Conversely, if we are passionate, we cannot engage in subtle reasoning. There seems to be a fixed amount of force that the mind has, especially when the activities are of “different natures,” as in the above examples: “the force of the mind is not only diverted, but even the disposition chang’d, so as to render us incapable of a sudden transition from one action to the other, and still more of performing both at once.” This explains why conviction is not affected as we move up to the higher levels of self-evaluation. “Belief, being a lively conception, can never be entire, where it is not founded on something natural and easy.”

12. This is the correct way of handling the matter. There is another way of dismissing skepticism “without enquiry or examination,” by presenting it with a dilemma.

The author says that any argument based on this dilemma is “not just.” He attacks the first alternative, saying nothing about the second. The idea of the first alternative is that strong skeptical arguments destroy themselves. [This is a claim that was made by the ancient skeptics.] But in destroying themselves, the author argues, they destroy reason along with them. In that case, they do not at all show the force of reason. To defend this claim, the author first assumes that skeptical reasonings are possible to exist, i.e., that their subtlety does not destroy them, as the author himself has argued that they do. Then there is a contest between reason and the skeptical arguments. Reason starts out the stronger and in fact is the only source of materials on which the skeptic can draw. The force of the skeptical arguments is backed up by reason, even as they attempt to undermine it. Reason gives the skeptical arguments a “patent,” but the patent is one which in turn undermines reason. So the value of the patent for the skeptical argument is diminished. Both reason and the skeptical argument lose value. As the process continues, the force of both reason and the skeptical arguments are diminished, “till at last they both vanish away into nothing.” If “dogmatical” reason is strong, so is the skeptical argument to which it lends force. If it is weak, skepticism is weak as well. Neither loses any force in the contest “without taking as much from its antagonist.” The bottom line, then, is that skeptical arguments need to be broken to protect reason, and, happily, nature does this for us, keeping the skeptical arguments from having any real influence on us.

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