David Hume, a Scottish philosopher in the 18th century, is famous for skepticism on the objectivity of causality and validity of moral judgment. But his assertion that causes and effects, “is” and “ought” are distinct and the connections between them are uncertain because of their subjectivity puts the cart before the horse. The fact is that, as the subject encounter uncertain affairs, it must divide them into causes and effects or “is” and “ought” so as to reduce uncertainty.
1 : Humean skepticism on objectivity of causality
What is essential for an object to be a cause of another? According to Hume, contiguity, succession and necessity are essential. Hume doubted the objectivity of causality. In fact we cannot perceive the tie by which causes and effects are united. We can infer, if not directly perceive, contiguity and succession from what we perceive more easily than necessity. From what can we then infer the necessity of causality? Hume thinks it is a frequent repetition of an object after another.
For after a frequent repetition, I find, that upon the appearance of one of the objects, the mind is determin’d by custom to consider its usual attendant, and to consider it in a stronger light upon account of its relation to the first object. ‘Tis this impression, then, or determination, which affords me the idea of necessity.
If the relation between causes and effects is a subjective connection, its necessity is not objective and a cause might produce an effect different from the usual one.
When I see, for instance, a billiard-ball moving in a straight line towards another; even suppose motion in the second ball should by accident be suggested to me, as the result of their contact or impulse; may I not conceive, that a hundred different events might as well follow from that cause? May not both these balls remain at absolute rest? May not the first ball return in a straight line, or leap off from the second in any line or direction? All these suppositions are consistent and conceivable. Why then should we give the preference to one, which is no more consistent or conceivable than the rest? All our reasonings a priori will never be able to show us any foundation for this preference.
Is this Humean skepticism right? I think the necessity of the connection is not a necessary condition to be the causal connection but a sufficient condition not to be the causal connection. It is not the case that the connection between causes and effects is uncertain because of its subjectivity but that the subject must divide an object into causes and effects because of its uncertainty. If a connection between a cause and an effect gets necessary, the cause and the effect will be regarded not as a cause and an effect but an object.
For example, although pushing a button of a remote controller causes TV broadcasting, we usually describe it just “turning on a TV”. When do we then divide this one object into two, pushing a button of a remote controller and the start of TV broadcasting? It is when we face uncertainties, that is to say, when we are not accustomed to a remote controller, when we have it repaired and so on.
The division into two is sometimes insufficient. According to Hume, causes must be contiguous to their effects. This means a chain of causes must link an effect to a cause, if the latter is remote from the former.
Tho’ distant objects may sometimes seem productive of each other, they are commonly found upon examination to be link’d by a chain of causes, which are contiguous among themselves, and to the distant objects; and when in any particular instance we cannot discover this connexion, we still presume it to exist. 
How far must we divide the chain and how contiguous must the minimum unit of a cause and an effect be, then? To a scale of an atom or quark? Instead of being lost in such a scholastic maze, we should reconsider the original motive of our dividing causes and effects. Now that the division is motivated by the reduction in uncertainty, the chain should be divided until we can dispel it.
Let’s return to the example of the remote controller. When pushing a button on a remote controller stops turning on a TV and it is not what you expect, you experience an increase in uncertainty and you must divide the object into a chain of causes in order to find a true cause of malfunction. Thus you divide the simple chain,
pushing a button of a remote controller >> turning on a TV
into a more complex one,
pushing a button of a remote controller >> carrying electricity to its semiconductor >> a near infrared diode emitting a beam of light >> sensors on the receiving device picking up the beam >> integrated circuit processing the signal >> turning on a TV
and confine the true cause of uncertainty to a smaller segment of the uncertain whole, as if, when an infectious disease is prevalent, we try to find the infected and isolate them to prevent the disease from spreading.
Uncertainty is the state that can be otherwise than is expected. In order to reduce the uncertainty, our information system called intellect divides the object that can be otherwise than is expected into a chain of causes, verifies that each causal connection cannot be otherwise than is expected and finds the part that is otherwise than is expected. If you notice the diode is broken, you can reduce uncertainty by replacing it with a new one. Once the situation cannot be otherwise than is expected, the chain of causes shrinks like an accordion and turns into a single object “turning on a TV”.
2 : Humean skepticism on validity of moral judgment
Hume is also famous for skepticism on deriving “ought” from “is”. The assertion quoted below is said to take the lead of the 20th century meta-ethics arguments that makes a sharp distinction between fact and value.
In every system of morality, which I have hitherto met with, I have always remark’d, that the author proceeds for some time in the ordinary ways of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when all of a sudden I am surpriz’d to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, ’tis necessary that it shou’d be observ’d and explain’d; and at the same time that a reason should be given; for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it. But as authors do not commonly use this precaution, I shall presume to recommend it to the readers; and am persuaded, that this small attention wou’d subvert all the vulgar systems of morality, and let us see, that the distinction of vice and virtue is not founded merely on the relations of objects, nor is perceiv’d by reason.
Humean skepticism on the conventional moral philosophy that have tried to derive “ought” from “is” of necessity is similar to that on the conventional natural philosophy that have tried to derive effects from causes of necessity and we can find a similar reversion here. That is to say, Hume thinks that, since “is” and “ought” are quite different and the connection between them is subjective, it has no objective necessity. In fact, it is the other way around: since its necessity is called into question, the subject must divide it into “is” and “ought” and recombine them to reduce its uncertainty. If you feel the connection between “is” and “ought” necessary, they must keep intuitive unity.
To take an illustration, murder is a bad thing beyond question for ordinary people, who cannot kill others without trembling and agony. At this intuitive level, the fact “It is murder” is inseparable from the duty “I ought not to do it.” In a special situation, however, say, on the battlefield where your hesitation in killing the enemy is likely to result in death of your side, the intuitive unity of the fact and the duty collapses and you must separate the fact from the duty.
But this separation increases uncertainty, because it follows that murder is sometimes wrong and sometimes not. To reduce this uncertainty, you must divide the fact that can be otherwise than is expected into segments, verifies that each connection with the duty cannot be otherwise than is expected and finds the part that is otherwise than is expected. If you conclude that we must not kill others unless the killing can prevent killing us, you can reduce the uncertainty.
3 : Uncertainty precedes the division into elements
It is not the certainty but the uncertainty that makes us conscious of the connection between causes and effects and the division into them itself is motivated by the reduction in uncertainty. Likewise it is not the certainty but the uncertainty that makes us conscious of the connection between “is” and “ought” and the division into them itself is motivated by the reduction in uncertainty. Generally speaking, an increase in uncertainty motivates a conscious system to divide a single whole object into elements to reduce the uncertainty and, after the division is complete, the system tends to think that first there are elements and then complexity (uncertainty) arises from the combination between them.
I know that the ontological relation between cause and effect corresponds to the deontological relation between means and purpose and the axiological relation between fact and value is similar to the epistemological relation between fact and truth. In this sense my comparison between Humean skepticism on the objectivity of causality and his skepticism on validity of moral judgments may not be strict. But the generalization of Humean reversion makes this difference unimportant.
We can find Humean reversion in the conventional explanation by systemics researchers. They have explained uncertainty in terms of complexity, the number of combinations of elements. This explanation forgets the original arche of philosophy. It is not the case that an increase in elements increases the complexity and makes systems to reduce the complexity but that an increase in uncertainties makes systems to divide uncertainties into elements in order to reduce them.
In the Middle Ages alchemy was in fashion. They tried to transform copper and other base metals into gold, only to fail. The uncertainty of the world for those who believed in magic and alchemy was high. Modern chemistry reduced this uncertainty by dividing chemical compounds into chemical elements and showed that alchemists can only change compounds and cannot make new elements like gold from other elements. First there were not elements but uncertainties and the division into elements reduced the uncertainty of predicting chemical reactions.
It is true that the number and sorts of elements increases complexity but the complexity has only the reduced uncertainty, which is much lower than that before the division into elements. When systemics researchers talk of complexity, its uncertainty has been already reduced to a considerable degree. We should not forget that the original arche for systemics is not elements but uncertainty.
4 : References
- A Treatise of Human Nature, Book1. Part3. Section2. (author) David Hume
- A Treatise of Human Nature, Book1. Part3. Section14. (author) David Hume
- An Enquiry Concerning Human Understanding, Section4. Part1. (author) David Hume
- A Treatise of Human Nature, Book1. Part3. Section2. (author) David Hume
- A Treatise of Human Nature, Book3. Part1. Section1. (author) David Hume