What does Kant mean by "intuition"? I've been reading a small book by Jaspers on Kant's whole philosophy, but he is so unclear about this word "intuition" and the word seem important in some way to what Kant is saying.

You are absolutely right that Kant's conception of intuition is crucially important to the argument of the first Critique. It is, however, quite difficult exactly to say what intuitions are, for Kant.

In the Transcendental Aesthetic of the first Critique, Kant writes: "In whatever way and through whatever means a cognition may related to objects, that through which it relates immediately to them, and at which all thought as a means is directed as an end, is intuition. This, however, takes place only insofar as the object is given to us; but this in turn, is possible only if it affects the mind in a certain way. This capacity...to acquire representations...is called sensibility. Objects are therefore given to us by means of sensibility, and it alone affords us intuitions..." (A 19/B 33).

Here's a start at understanding Kant's conception of intuition: intuitions are representations, given in sensation, that provide the material--the starting point--for all cognition.

Allow me to add a brief note to Sean's answer.

'Sensibility' translates 'Sinnlichkeit', which isroughly the ability to have intuitions; it is thus contrasted withthe understanding, which is the ability to have (and employ)concepts. 'Sensation', however, translates 'Empfindung', andmeans roughly what it does in English: the stimulation of one'ssenses by the real presence of an object affecting them. The point ofsaying this is that the two concepts of sensibility and sensation arenot etymologically related in German as they are in English. Thestandard English translations are thus misleading and disguisethe fact that Kant is speaking of two very different things. Forexample, sensibility includes the ability to imagine – that is toform intuitions of things that are not actually there – and stillmore importantly, to have 'pure' intuitions of mathematical objects(e.g. a circle) – which of course could never be there as physicalobjects affecting me. It is precisely because of the difference fromsensation that Kant believes he can discover an a priori, formaldimension of intuition. So, I suggest we define intuition withoutreference to sensation as: an immediate, singular representation inspace and time.

A most interesting question from long ago, and two good answers! I don't know if you are interested in a more detailed response, but in case you are I'll add some more details. Please ignore if this is too much for your interests, and please understand that, as both Sean's and Douglas's responses make clear, this is difficult exegetical territory and so different critics will have different takes on this fascinating topic.

First, here's my gloss on 'intuition,' drawing upon two passages on Kant's First Critique, one of which Sean quoted above:

[A19/B33] Intuitions are one of two sorts of representations which we syn­thesize to form experience; they are connected with the sensibil­ity (concepts are the other sort of representation; they are con­nected with the understanding). Through intuitions, "objects are given to us by means of sensibility". Intuitions rest on "affectations": objects affect our mind in certain ways in which we are "receptive"; in us are produced "sensations" and thereby we "receive representations", viz. intuitions. Since "in no other way can an object be given to us...all thought must...relate ulti­mately to in­tuitions". Intu­itions are the only sort of representations which "relate immediately to the object".

[A50/B74] However, there is another type of intuition, namely pure intu­itions. For Kant, representations which "contain sensation" are empirical; in cases where there is "no mingling of sensation" representations are pure. Thus some intuitions--the pure ones--are not connected with affectations and sensation. Rather, "pure intuition...contains the form under which something in intuited". For us, space and time are pure intuitions; these are a priori conditions on our sensibility which determine exactly how we are "receptive" to affectations. Because Kant argues that our representation of space must be of space as a whole, we have a pure intuition and not a pure concept.

Second, about sensibility, which in general I would define as the the faculty of intuitions, which is opposed to the faculty of con­cepts, the understanding. Sensibility can also be viewed as the faculty of receptivity (i.e., to the action of affecting objects on our minds), in which case it is opposed to the understanding as the faculty of spontaneity. There are laws of sensibility which presumably limit our possible experience according to the way in which we are re­ceptive, i.e. which determine laws of intuition" which intuitions pos­sible for us must fulfill. Thus, the sensibility is one source consti­tuting our ability to make and have representations; the other is the under­standing (that is, both supply the limits of our possible expe­rience).

[A19/B34] Thus, in the beginning of the Aesthetic, sensibility is defined as "the capacity (receptivity) for receiving representations through the mode in which we are affected by objects". Kant's idea is that objects are given through the sensibility (in intuitions), they are thought through the under­standing (through concepts), and our experience of them comes from judg­ments (which involve the synthe­sis of intuitions and concepts in the unity of apperception). (For Kant, intuitions are representations of empirical objects, as--indeterminate--appearances.)

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