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Kant on Causality: A Critical Approach
Jan 1, 2011

Immanuel Kant shaped modern philosophy enormously and determined its way towards today. There are two main strands in contemporary Western philosophy: analytic philosophy, which is widely practiced in Anglo-Saxon World, and Continental philosophy, which is centered in continental Europe. Both traditions refer to Kant as a common root. Kant’s ideas were very influential in the modern period and still draw attention of many intellectuals today. In order to understand the contemporary intellectual world, we should carefully examine Kant’s ideas.

Even though Kant has very original insights that opened new gateways in the history of philosophy, his so-called “critical philosophy” is not devoid of defects. This article aims to present Kant’s account of causation and critically evaluate it.

Kant’s famous remark about his awe for “the starry heavens above me, and the moral law within me,” which is written in his gravestone, shows his orientation in philosophy. While he was interested in explaining the features of the universe and the nature of our theoretical knowledge, he did not ignore the practical aspect of our life that concerns with how to act in the right way. That is to say, ethics and natural science were main disciplines Kant tried to understand. However, this paper examines his analysis of theoretical knowledge and the natural science by focusing on his account of causality.

An introduction to Kant’s “critical philosophy”

Before Kant, there were two important traditions in modern philosophy: rationalism and empiricism. On the one hand, the rationalists assumed that we could obtain knowledge of the world by trusting in the power of our minds. Kant considered them to be dogmatic in the sense that they dogmatically assumed this idea without examining the nature and limits of our minds so as to see whether we can really achieve this goal or not. On the other hand, the empiricists usually distrusted the power of the mind in its attempt to know the world, and in its most extreme case, in Hume, it led to skepticism. In response to these two approaches, Kant suggested to examine critically the nature and limits of the mind and see to what degree we can have knowledge at all. This is called “critical philosophy.”

For Kant, our minds are not passive receivers of representations like mirrors. A normal flat mirror reflects the image from an object as if it is the same except in a two-dimensional way. It was a common attitude among philosophers before Kant to treat the mind like a mirror. The mirror does not change the form of the object. Likewise, the mind does not affect or change the form of the objects, it just receives them. However, Kant changed the whole picture. He treated minds as active filters. Whatever is reflected on it is shaped in a certain way. On this view, the mind is like a concave or convex mirror, or colormatic glasses but it is not like a flat mirror.

According to Kant, the mind has three faculties with different functions. These faculties are sensibility, understanding and reason. Through sensibility we get the raw material of experience. This material is structured and shaped by space and time which are not outside the mind but are the pure forms of the faculty of sensibility. What we get through this faculty is called “intuition.”

The faculty of understanding provides us with concepts, especially with “the pure concepts,” or categories, of which there are twelve in total, and are used in organizing the intuition. In brief, what is reflected on the mind as coming from the world is structured by the a priori forms of intuiton (space and time) to which the twelve categories of mind are applied.

Kant’s postulation of the mind as an active factor in obtaining knowledge is considered to be “the copernican revolution” in philosophy. Kant has a formula which depicts his system very well: “Thoughts without content are empty, intuitons without concepts are blind.” In order to have understanding, we should both have intuition and concepts. These two conditions should be fulfilled for a genuine and reliable understanding. First, concepts without intuiton do not give us understanding; we can just think about them and never be sure whether they are something about real or not. According to Kant, concepts such as soul, God, and free will are ideas to which no intuition corresponds. Second, if there were no ordering role of the mind, all the information we got from the world would be chaotic. For instance, we would not be able to identify a certain individual as a human being, an animal of a different sort or even as an object, because we lacked an ability to order and classify the information. Therefore, according to Kant, the world appears to us differently from as it is in itself due to the ordering character of the mind.

Kant calls the world as it appears to us “phenomena” and the world in itself “noumena.” The latter is beyond the limits of the legitimate realm of theoretical knowledge. We cannot understand it, and we cannot theoretically know anything about it: we can only think about it. Ideas such as those of God and free will are directed toward the nounemal realm. They belong to the faculty of reason and have a regulative role in ordering and unifying our experience. However, they are empty according to Kant. That is to say, there is no corresponding intuition to them in our experience. Thus, we cannot decide whether they really exist or not by theoretical knowledge. This conclusion of Kant’s critical philosophy may suggest an agnostic position towards God, (actually it led many people to become agnostics) according to which human beings can neither affirm nor deny the existence of God. However, Kant thought that he found a reason for believing in God in another domain, namely in practical reason and knowledge. Nevertheless, Kant’s attempt to show the illegitemacy of theoretical knowledge regarding neumena undermines itself. This can be seen especially in his analysis of causality.

Synthetic a priori truths

Kant takes mathematical science and natural science for granted. He accepts them as successful sciences and tries to understand the conditions under which they are possible. His conclusion is that these sciences can be grounded only on “synthetic a priori judgments.” There are two important conceptual distinctions here: the analytic-synthetic and the a priori-a posteriori. The former is a semantic distinction, the latter is epistemological. A statement is analytic if its predicate-concept is included in the subject-concept, otherwise it is synthetic. The proposition that all black cats are black or that bachelors are unmarried is analytic. A black cat is black, the predicate is embedded in the subject here. And bachelors are by definition unmarried because a bachelor is a single male. However, the color of my cat is not included in its definition. A priori judgments are known independently of experience whereas a posteriori ones are known by appealing to experience as a justification. We know that everything is identical to itself without any experience. But we need some experiential evidence to affirm the statement that the Morning Star is identical with the Evening Star. It was a scientific discovery that those stars were actually the same, namely Venus.

For Kant, all analytic judgments are a priori. He also claims that there are synthetic a priori statements. This is a bit unusual because we normally know synthetic statements by experience. How can we know a statement a priori if its predicate is not included in the subject? Kant explains the possibility of such judgements by appealing to the mind’s role in shaping experience. According to him, by applying the categories to intuition, we put what is in our minds into our experiences. So, “we can cognize of things a priori only what we ourselves have put into them.” In other words, the categories shape the experience and we know that aspect of experience a priori since it belongs to us. The conceptual distinctions presented so far enable us to understand Kant’s account of causality better.


From a historical point of view, Kant’s account of causality was a response to Hume’s scepticism about causation. Let us first see what Hume said about this issue. Hume points out that we only observe correlated events in nature, and that there are some regular correlations and some irregular ones. For instance, we always observe that lightning precedes thunder. On the basis such regular correlations, we infer that the events in question are also causally related. That is to say, lightning causes thunder. However, according to Hume, we never observe causation between events. What is observed is just that two events are correlated in a regular manner. Causation is what our mind is inclined to infer when faced with such regularities. Causal links are produced by the human mind as subjective mental operations. So, there is no objective causality between events: it is our subjective interpretation of the regularity between them.

If we consider the fact that electrical charges are regarded as the common causal factor behind lightning and thunder by contemporary scientists, we can appreciate what Hume said. We do not observe causal links. Perhaps, sometime in the future, scientists will propose another physical factor as the cause for thunder, lightning and maybe for electical charges. Since we do not observe causal links, we can never be sure about what causes what. Hume extends this skepticism so far that nothing really causes anything else. There is no objective causation; there are just correlations in our experience. In other words, he also denies the objectivity of the universal causal principle, namely that every effect or event must have a cause.

As a response, Kant distinguishes two different levels in analysing causation. On the one hand, he tries to prove the objectivity of the universal principle of causality. Kant is aware of the difficulty of proving it on the basis of experience. Such a universal principle cannot be based on experience. Kant considers this univeral principle as a synthetic a priori truth. It is valid for anything we experience because all our experience is shaped by the category of causality. He formulates this principle in the following way: everything that happens presupposes that which it follows in accordance with a rule.

According to Kant, the phenomena consisting in irreversible sequences indicate the causal order. As an example of irreversible sequence, he mentions the sequence when we look at a ship moving down the river. In this case, what we apprehend is an objective process. And its order cannot be arranged otherwise than in this very succession. So, when we watch the ship’s departure, the order in which our visual states occur is not up to us. As a conclusion, Kant argues that in irrevesible cases, the apprehension of one perception which occurs necessarily succeeds that of the other which preceded according to a rule called “the law of the connection of cause and effect.”

On the other hand, Kant’s analysis of irreversible sequences does not suggest anything about particular causal relations. A particular sequence of irreversible representations does not enable us to identify the cause of the event in question: it only indicates that the event in question must have a cause (in the sense that some other event precedes it), even if we do not know what this cause is. Kant expresses this point by saying that “Everything in nature, as well in the inanimate as in the animated world, happens or is done according to rules, though we do not always know them....”

While there are some ambigious passages indicating as if Kant has identified some necessary causal links between particular events (such as that the sunshine caused the warmth of a stone), those passages should be interpreted under the light of this general statement here. The reason simply is that Kant aims to exemplify his view of causation in such contexts rather than identifying some particular causal links.

A fundamental problem with Kant’s analysis of causality

As we have seen, Kant treats the universal principle of causality as a synthetic a priori truth. In doing so, he limits causal ascriptions to the phenomenal realm because it is the phenomenal realm not the noumenal realm, which is shaped by our minds. So, according to Kant causal talk about noumena, things in themselves, is not legitimate and does not give us theoretical knowledge.

However, the question that should be answered in this regard is if the human mind interacts with noumena. If so, how does it interact? In some passages, Kant seems to consider noumena to be an empty and limiting concept. We cannot know anything about this realm (even whether or not noumenal objects such as free will, soul and God exist), therefore it is just a heuristic device indicating what is beyond our theoretical knowledge. Thus, we cannot say anything about the relationship between the mind and noumena, because noumena are beyond our understanding. Otherwise, anything we say can only be an illegitimate speculation.

Nevertheless, such passages do not represent Kant’s whole philosophical outlook. As a fundamental aspect of his critical philosophy, Kant assumes that our experience is shaped by us but not totally created by us. There is an external element to experience that is independent of us. He must accept that there are noumenal objects even though we do not know what they are. They are not just conceptual tools formulated to define the phenomenal realm. In fact, there are several passages in which Kant explicitly ascribes causal efficiency to the noumenal realm.

For instance, when Kant distances himself from the idealist philosophers who claim that everything we perceive is mind-dependent and there is no objective reality outside the mind, he claims that “there are bodies without us, that is, things which, though quite unknown to us as to what they are in themselves” and that we know them “by their representations which their influence on our sensibility procures us.”

As another example, this time regarding the free will of human beings, Kant thinks that human beings are free with respect to the noumenal realm but under causal determination with respect to phenomenal realm. When he tries to account for moral responsibility, he presents the free will as having its own causal power to be able to appropriate particular human actions. The following is an explicit remark: “The will is a kind of causality of living beings so far as they are rational.”

As it is clearly seen, Kant is forced to accept that the realm of things in themselves (noumena) causes the realm of appearances (phenomena) and this is exactly what undermines the very foundation of his critical project as limiting theoretical knowledge to phenomena.


Kant certainly has an insight in making a distinction between phenomena and noumena; however, his way of distinguishing these two realms undermines his own critical philosophy. There is a similar distinction made by Muslim theologians between dhahir (phenomena) and batin (noumena). In their case, categories of causality and existence for instance are legitimately applicable to noumenal realm, but they argue that we do not know how they are applicable. According to them, for instance, we know that God exists but we do not know how He exists. His existence is quite different from our existence. As Descartes says: “A finite mind cannot grasp [adequately] God, who is infinite. But that does not prevent [the finite thinker] having a perception of God, just as one can touch a mountain without being able to put one's arms around it.” As a conclusion, Kant’s distinction between phenomena and noumena should be improved so that it enables us to ascribe existence and causality to the noumenal realm even in a minimal sense.