I am trying to self-study a bit of philosophy. I am an applied mathematician by trade, and am therefore drawn to Kant's work on the limits of human knowledge, in particular his exchange with Hume. I was wondering if anybody could clarify a point for me:

As far as I understand it, Kant agrees with Hume to the extent that we can never know the true nature of things such as causation, which Hume argues may not exist at all. Now, Kant takes this skepticism a step further by saying that we don't even observe the "real world" at all, only a representation of it in our minds. However, in doing so, he somehow saves the existence of causation. This is where I could use some help. Here is my first attempt to understand what Kant is saying:

What Kant is saying is that the mind has certain methods of structuring the data it receives ("forms of intuition") in order to paint our mental pictures. These include notions of space, time, causation, etc. From here, he uses a sort of Descartes "I think therefore I am" to these forms of intuition. That is, causation is a fundamental tool for structuring how I perceive the world, therefore causation exists, at least in this sense.

Is this a rough idea of what is going on? Thanks in advance!

  • Having Trouble with Kant. philosophynow.org/issues/86/Having_Trouble_With_Kant
    – Gordon
    Commented Nov 2, 2019 at 17:55
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    Kant "saves" causality by making it a bit more than mere Hume's association by habit, but he only saves it as an a priori principle of structuring our experience, not as "really" existing "in itself". SEP Kant and Hume on Causality should help clarify the finer points.
    – Conifold
    Commented Nov 2, 2019 at 23:42
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    @Conifold Thank you. And I think this gets to my point, so I want to make sure I understand. Kant described two worlds, the "real world", and the one we perceive. Does Kant conclude that causality must actually exist in the real world? Or just as a structuring mechanism in our minds?
    – Mark
    Commented Nov 3, 2019 at 2:21
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    Kant does not describe the "real world". That is his "thing in itself", and the most we can say about it is that it exists, if that. The reason is that the categories we use to think and talk (including real, thing and existence) are categories of our experience, the world of appearances, and are empty beyond that. The world of appearances is grasped through two inputs, undifferentiated sense intuitions, and a priori concepts, the categories, that frame them. Causality is one such category. To Kant, categories are absolute and universal, hence beyond merely mental, but yes, they come from us
    – Conifold
    Commented Nov 3, 2019 at 3:09
  • Simply stated- Kant ascribed to the reality in the function of reason. Hume was entirely skeptical that reason as a function even exists. CMS
    – user37981
    Commented Nov 4, 2019 at 21:01

3 Answers 3


Perhaps the major difference is that Hume derives from experience whatever categories he uses - or supposes that he does so. To take causation as a star example: Hume derives the category of causation from experience in the following way. When event A is prior to event B (priority); when A and B are close in space and time (contiguity); and when A-type events are regularly followed by B-type events (constant conjunction): then by the association of ideas we assume that event A causes event B.

This is Hume's essential picture. Kant's picture is radically different. For Kant, we do not derive the category of causation from experience. Rather, it is a part of the cognitive apparatus of the mind that we bring to experience. It is only by means of an inherent network of categories, such as causation, that coherent experience is possible for us. In other words, for Kant, Hume is precisely wrong. There is not, first experience and then the derivation of the category of causation from experience. On the contrary there is first the category of causation and this structures (or plays a role in structuring) experience in such a way that we can even think of A-type or B-type events.

Causation, involving (unless we get into really technical science) the priority of the cause to the effect, and contiguity, closeness in space and time, between cause and effect, presuppose space and time: these 'forms of intuition' (or roughly 'forms of representation') are not empirical in origin and we do not derive them from experience. On the contrary, again, unless we already had these forms of intuition we could not order or locate events in time and space.

This is a highly brief account, with endless details missing, but it may serve to the fundamentally different approach between Hume and Kant as regards experience and the empirical.


Hume was deeply skeptical of metaphysics. For a non-philosopher this includes topics such as being, essence, substance, space, time, the self, and causation.

For example: in A Treatise of Human Nature Hume argues that we have no innate concept of Cause and Effect (C\E) and that C\E is not rationally known but instead we develop the concept of it through the near universal juxtaposition of two events.

For Hume our knowledge of metaphysical subjects is not rational, but is caused by non-rational mechanisms in the mind and we do rely on them, especially time, space, C\E, and the self. But they are not uniquely privileged and thus cannot provide certainty for our beliefs. Also,they may properly be subjected to skeptical critique.

This has significant implications for both science and religion. And the religious authorities of his day saw his work on causation as an attack on the foundations of religious belief. That was before he published his work on miracles, or his famous polemics against popular religion.

Kant read at least books I & II of Hume's Treatise(in translation) but he was not entirely persuaded and wanted to save metaphysics. At least a little bit. Kant argued in The Critique of Pure Reason that for us to have an experience, the mind must impose certain structures on incoming sensory data. These impositions are "known" a priori (before experience) and thus are metaphysical, and to an extent privileged. There aren't many of these beliefs but they include time, extension (space), the self, and Cause and Effect. Kant also believed in universal and immutable laws, something Hume denied.

Speaking broadly: Hume tried to trash metaphysics while Kant tried to save parts of it. Kant's theory of a priori truths --especially his theory of synthetic a priori truths-- is fundamentally incompatible with Hume's more empirical approach. Hume is traditionally seen as the more skeptical of the two.

Also, Hume, before Kant, argued that we cannot get to the object-in-itself, even if he did not use that terminology. For Hume the mind operates on impressions and ideas. They start with sensory perceptions, but there is no guarantee that this are correct or accurate.

Here is an exert from Hume's Treatise Book I, Part II, Section VI: The Idea of existence and of external existence.

"nothing is really present with the mind but its perceptions or impressions and ideas, and that external objects become known to us only by those perceptions they occasion [...] it follows that tis impossible for us so much as to conceive or form an idea or anything specifically different from ideas and impressions [...] the farthest we can go towards a conception of external objects ...is to form a relative idea of them without pretending to comprehend the related objects."

You aren't a lone in struggling with Kant. He was a terrible writer. I once heard a Kantian say that every English translation of the Critique sucks, because the German sucks. Despite that, make sure you are reading a decent translation. Guyer/wood is recommended or Pluhar. Kemp Smith is considered dated at this point, but his translation was the standard for at least a generation or two of Kantian scholars.

Reference to secondary literature may help. The Blackwell Companion to Kant may be a good place to start. Or the Stanford Encyclopedia of Philosophy


The answer to "Is this [as you described it] a rough idea of what is going on [with Kantiam metaphysics] is an unequivocal: Yes. Though your characterization "From here, he uses a sort of Descartes "I think therefore I am" to these forms of intuition" is ambiguous -- but if if what you mean is this and only this instantiates thought as we homo sapiens know it, then yes.

Kant identifies the forms (innate intuitions) of space and time, and twelve pure concepts of the understanding (ontological predicates): unity, plurality, and totality for concept of quantity; reality, negation, and limitation, for the concept of quality; inherence and subsistence, cause and effect, and community for the concept of relation; and possibility-impossibility, existence-nonexistence, and necessity and contingency for the concept of modality.

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