Kant presents an account of how we intuit () objects and accounts of space and of time. Before Kant, some thinkers, such as
Leibniz, had come to the conclusion that space and time were not things, but only the relations among things. Contrary to thinkers, including Newton, who maintained that space and time were real things or substances, Leibniz had arrived at a radically different understanding of the universe and the things found in it. According to his
Monadology, all things that humans ordinarily understand as interactions between and relations among individuals (such as their relative positions in space and time) have their being in the mind of God but not in the Universe where we perceive them to be. In the view of realists, individual things interact by physical connection and the relations among things are mediated by physical processes that connect them to human brains and give humans a determinate chain of action to them and correct knowledge of them. Kant was aware of problems with both of these positions. He had been influenced by the physics of
Newton and understood that there is a physical chain of interactions between things perceived and the one who perceives them. However, an important function of mind is to structure incoming data and to process it in ways that make it other than a simple mapping of outside data. Gottfried Martin says: The salient element here is that space and time, rather than being real
things-in-themselves or empirically mediated appearances (), are the very forms of intuition () by which we must perceive objects. They are hence neither to be considered properties that we may attribute to objects in perceiving them, nor substantial entities of themselves. They are in that sense subjective, yet necessary, preconditions of any given object insofar as this object is an appearance and not a
thing-in-itself. Humans necessarily perceive objects as located in space and in time. This condition of experience is part of what it means for a human to cognize an object, to perceive and understand it as something both spatial and temporal: "By
transcendental idealism I mean the doctrine that appearances are to be regarded as being, one and all, representations only, not things in themselves, and that time and space are therefore only sensible forms of our intuition..." Kant argues for these several claims in the section of the
Critique of Pure Reason entitled the "Transcendental Aesthetic". That section is devoted to inquiry into the
a priori conditions of human sensibility, i.e. the faculty by which humans intuit objects. The following section, the "Transcendental Logic", concerns itself with the manner in which objects are thought. == Schopenhauer ==