Descartes thought that he had solved the problems of knowledge with his Cartesian Method. In reality, he did not. The particular rationalist epistemology that he developed was later dismantled by empiricist theorists like David Hume.For David Hume, all knowledge stemmed from sense perception and it can be the only criterion for knowledge. Sense perception refers to something empiricial, something that could be observed or experienced through senses, hence the name empiricist epistemology.
According to empiricist epistemology, we cannot establish the truth of any a priori knowledge without referring back to the knowledge itself, which would be the fallacy of circular logic. Hume, however, faced exactly the same problem with his starting point of knowledge, that is, the sense perception. What establishes its truth/validity? How do we know for sure what we experience through our senses does in fact exist out there? Recall from the previous post, the problem of distinguishing dream from reality. Hume doesn't give us any objective solution to get out of this problem. In the next post, you'll see that Berkeley, the Idealist philosopher, makes a similar criticism of sense perception.
Taken to its logical extreme, Hume's empiricist epistemology, as Shaheed Sadr argues, leaves us nothing but a form of nihilism, which is obviously not very helpful. Causality is one of the those fundamental problems that Hume had taken up but was unsuccessful in solving it due to the limitations of his epistemological method. See below.
Shaheed Sadr writes:
Causality as a Conceptual Idea
"David Hume, one of the advocates of the empirical principle, was more precise than others in applying the empirical theory. He knew that causality, in the real sense of the term, cannot be known by the senses. Because of this, he rejected the principle of causality and attributed it to the habit of the association of ideas, saying that I see the billiard ball move, and then encounter another ball that, in turn, moves. But in the movement of the former ball, there is nothing that reveals to me the necessity of the movement of the latter. The internal senses also tell me that the movement of the organs follows upon an order from the will. However, they do not give me a direct knowledge of a necessary relation between the movement and the order.
But the rejection of the principle of causality does not at all minimize the difficulty that faces the empirical theory. The rejection of this principle as an objective reality means that we do not believe that causality is a law of objective reality, and that we are unable to know whether the phenomena are linked by necessary relations that make some of them effects of some others. However, the principle of causality as an idea assented to is one thing, while the principle of causality as a conceptual idea is another. Suppose, for example, that we do not assent to the fact that some sensible things cause some other sensible things, and that we do not form an assent concerning the principle of causality, would this mean that we do not have a conception of the principle of causality either? If we do not have such a conception, then what is it that was rejected by David Hume? Can a human being reject something of which he has no conception?
The undeniable truth is that we conceive the principle of causality, whether or not we assent to it. Further, the conception of causality is not composed of the conceptions of the two successive things. When we conceive the causation of a specific degree of temperature for boiling, we do not intend by this causation an artificial composition of the idea of temperature and that of boiling. Rather, we intend a third idea that exists between the two. From where, then, does this third idea that is not known by the senses come, if the mind does not have the ability to create non-sensible ideas? We face the same difficulty with regard to the other notions mentioned earlier; since all of them are non-sensible. Thus, it is necessary to cast aside the purely empirical explanation of human conceptions and to adopt the dispossession theory (nazariyyat al-intiza)."
Source: Our Philosophy by Baqir Sadr. Trans. Shams C. Inati. See part I chapter I "The Primary Source of Knowledge".
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Causality as a Principle
"Fourth, the principle of causality cannot be demonstrated by means of the empirical doctrine. As the empirical theory is incapable of giving a sound justification of causality as a conceptual idea, so also is the empirical doctrine incapable of demonstrating it as a principle or an idea of assent. For experience cannot clarify anything to us except a succession of specific phenomena. Thus, by means of it we know that water boils when it is heated to 100 degrees [centigrade], and that it freezes when its temperature reaches below 0 degrees [centigrade]. As for one phenomenon causing the other, and the necessity between the two, this is something not disclosed by the means of experience, regardless of how precise it is and regardless of our repetition of the experience. But if the principle of causality collapses, all the natural sciences also collapse, as you will learn later.
Some empiricists, such as David Hume and John Stuart Mill, have admitted this truth. That is why Hume interprets the element of necessity in the law of cause and effect to be due to the nature of the rational operation that is employed in reaching this law. He says that if one of the operations of the mind is employed for the purpose of obtaining this law - adding that if one of the operations of the mind always leads to another operation that follows it immediately -then, with the passage of time, a constant strong relation, which we call 'the relation of association of ideas', develops between the two operations. This association is accompanied by a kind of rational necessity, such that the idea that is linked to one of the two mental operations occurs in the mind, as does the idea that is linked to the other operation. This rational necessity is the basis of what we call the necessity that we grasp in the link between the cause and the effect. There is no doubt that this explanation of the relation between the cause and the effect is incorrect for the following reasons.
First, from this explanation, it follows that we do not reach the general law of causality except after a series of repeated events and experiments that fasten in the mind the link between the two ideas of cause and effect, even though that is not necessary. For the natural scientist is able to infer a relation of causality and necessity between two things that occur in one event. His certitude is not at all strengthened [later] beyond what it was when he observed the event for the first time. Similarly, the relation of causality is not strengthened by the repetition of other events involving the same cause and effect.
Second, let us put aside two successive external events and turn our attention to their two ideas in the mind - namely, the idea of cause and that of effect. Is the relation between them one of necessity or one of conjunction, as our conception of iron is conjoined to our conception of the market in which the iron is sold? If it is a necessary relation, then the principle of causality is confirmed, and a non-empirical relation between two ideas - that is, the relation of necessity - is implicitly admitted. [In this case], whether necessity is between two ideas or between two objective realities, it cannot be demonstrated by sense experience. If, on the other hand, the relation is a mere conjunction, then David [Hume] did not succeed in explaining, as he intended, the element of necessity in the law of cause and effect.
Third, the necessity, which we grasp in the relation of causality between a cause and an effect, involves no influence at all on requiring the mind to invoke one of the two ideas when the other idea occurs in the mind. That is why this necessity that we grasp between the cause and the effect is the same, whether or not we have a specific idea about the relation. Thus, necessity of the principle of causality is not a psychological necessity, but an objective necessity.
Fourth, the cause and effect may be completely conjoined, yet in spite of that, we grasp the causation of the one on the other. This is exemplified in the movement of the hand and that of the pencil during writing. These two movements are always present at the same time. If the source of necessity and causality were the succession of one of the two mental operations after the other by means of association, then it would not be possible in this example for the movement of the hand to play the role of the cause loll the movement of the pencil; for the mind grasps the two movements at the same time. Why then should one of them be posited as a cause and the other as an effect?
In other words, explaining causality as a psychological necessity means that the cause is considered as such, not because in objective reality it is prior to the effect and is productive of it, but because knowledge of it is always followed by knowledge of the effect by means of the association of ideas. Due to this, the former is the cause of the latter. This explanation cannot show us how the movement of the hand becomes a cause of the movement of the pencil, even though the movement of the pencil does not succeed the movement of the hand in knowledge. Rather, the two movements are known simultaneously. Thus, if the movement of the hand does not have actual priority and objective causality over the movement of the pencil, it would not have been possible to consider it as a cause.
Fifth, it is often the case that two things are associated without the belief that one of them is a cause of the other. If it were possible for David Hume to explain the cause and effect as two events whose succession we often grasp, such that a link of the type of association of ideas occurs between them in the mind, then the night and day would be of this sort. As heat and boiling are two events that have succeeded each other, until an associational link developed between them, the same must be true of the night and day, their succession and their association, even though the elements of causality and necessity that we grasp between heat and boiling are non-existent between the night and day. The night is not a cause of the day, nor the day a cause of the night. It is not possible, therefore, to explain these two elements by the mere repeated succession which leads to the association of ideas, as Hume tried to do.
We conclude from this that the empirical doctrine unavoidably leads to the elimination of the principle of causality and to the failure of demonstrating necessary relations between things. But if the principle of causality is eliminated, all the natural sciences will collapse, since they depend on it, as you will know."
Source: Our Philosophy by Baqir Sadr. Trans. Shams C. Inati. See part I chapter I "The Primary Source of Knowledge".
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"Let us therefore, ask: 'What is habit?' If it is nothing but a necessity existing between the idea of the cause and that of the effect, then it is another expression of the principle of causality.
If, on the other hand, it is something else, then it is not different from causality in being an invisible idea to which we have no corresponding sense perception or reaction. But Hume must reject this [view], as he rejects all the truths that are inaccessible to the senses. In criticizing the empirical doctrine earlier, a response was given to this unsuccessful explanation of causality attempted by Hume. Therefore, let that [response] be attended to."
Source: Our Philosophy by Baqir Sadr. Trans. Shams C. Inati. See part I chapter II on "The Value of Knowledge".
Note: Also see "The Principle of Causality" in the same book, part II, chapter III. Heisenberg's Uncertainty Principle is one of the topics that Shaheed Sadr discusses in this chapter, under the sub-heading "The Principle of Causality and Microphysics."
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