It will first be necessary to explain as distinctly as possible our opinion in regard to the fundamental constitution of sensible cognition in general, in order to preclude all misinterpretation of it.
We have therefore wanted to say that all our intuition is nothing but the representation of appearance; that the things that we intuit are not in themselves what we intuit them to be, nor are their relations so constituted in themselves as they appear to us; and that if we remove our own subject or even only the subjective constitution of the senses in general, then all the constitution, all relations of objects in space and time, indeed space and time themselves would disappear, and as appearances they cannot exist in themselves, but only in us.
What may be the case with objects in themselves and abstracted from all this receptivity of our sensibility remains entirely unknown to us. We are acquainted with nothing except our way of perceiving them, which is peculiar to us, and which therefore does not necessarily pertain to every being, though to be sure it pertains to every human being. We are concerned solely with this.
Through sensibility we do not cognize the constitution of things in themselves merely indistinctly, but rather not at all, and, as soon as we take away our subjective constitution, the represented object with the properties that sensible intuition attributes to it is nowhere to be encountered, nor can it be encountered, for it is just this subjective constitution that determines its form as appearance.
Immanuel Kant – Critique of Pure Reason