Human knowledge comes in two distinct forms. The first form is called a posteriori that is knowledge gained through experience. And the other form is called a priori which is knowledge gained without the help of experience. In between these knowledges, there is another rather complicated subtype of knowledge called a priori synthetic. Space and time are a priori synthetic. That is to say that although space and time are independent concepts in terms of the knowledge of their existence, they still inhabit a quality that enables us to observe them. A good example of a priori synthetic is the science of geometry that determines the dimensions of space synthetically but the knowledge of those dimensions is completely a priori. It is in that sense that Kant understands Space and Time as both empirically real and transcendently ideal.
To begin, Kant amplifies on the limits of experience. Knowledge gained empirically cannot nullify the fact that experience based knowledge is limited in its ability to explain all possible outcomes of an outer object. In Kantian words, “experience tells us, indeed, what is, but not that it must necessarily be so, and not otherwise.” (P 42, Smith) Therefore, it is crucial to have knowledge that is concrete and unchangeable by human experience. Space and Time are the only inhibitors of a priori knowledge and that quality is what makes them more reliable.
In defending Space, Kant claims that space is empirically real because of its relationship with the objects of our perception. In the section named “Conclusions from the above Concept” he makes clear the point that Space is empirically real because it contains as a container the objects of our perception. In other words, it would be impossible to imagine objects without the presupposed phenomenon of space. Kant also believes that Space is Transcendentally ideal. The first and foremost important reason is the fact that Space is underlying all of our “outer experiences.” Our intuitions drawn from our sensibilities are invisible without Space. In Roman numeral I of the “Space” section, he draws a distinction between things that exist through human perception and things that are presupposed by the human mind. Space is a presupposed phenomenon because the understanding or the “sensation” of Space is completely independent of our mind. In other words, unlike objects, Space does not require a process through which an object becomes a permanent part of our understanding. In essence, it is a presupposed and essential condition that must be present in order for any outer appearance to take place.
Another argument that helps establish Space as a priori knowledge is the argument number 2 in Kemp Smith's Edition. Objects that are definitely a product of human sensibility can leave a void in Space by being absent. But Space is something that remains in our minds ever after the disappearance of all outer appearances. This suggests that Space is a presupposed phenomenon that is not dependent upon concepts that are the constituents of a posteriori human imagination. This argument also leaves Space as empirically real because though it is presupposed and independent, we are still able to observe the difference between an empty and filled space. Moreover, the representation of the outer objects is dependent on Space because it is in space we are able to see or comprehend the different elements of an object. Without Space, it is impossible for any object to exist in a perceivable condition.
A passage that has made a lot of sense in terms of seeing Space as a Transcendently ideal but Empirically real phenomenon is the passage on top of page 74 in Kemp Smith addition. The complicated relationship of outer objects and Space is well defined:
That objects in themselves are quite unknown to us,
and that what we call outer objects are nothing but
mere representations of our Sensibility, the form
of which is space the true correlate of sensibility,
the thing in itself, is not known, and cannot be known,
through these representations; and in experience no
question is ever asked in regard to it.
This passage holds human understanding and Space as the source of all outer human experiences. The objects that are seen as constituents of human understanding or intuition are nothing but the result of spatial form due to which humans are able to see an object outside of them. Without which experience is virtually impossible because one can easily perceive an empty space but it is impossible to perceive any object outside of us without space.
Time is also empirically real but transcendently ideal. It is empirically known because of the observations one can make with the help of inner concepts. Through inner concepts, humans know that time has only one dimension. In argument number two of the “Time” section, Kant explains the empirical nature of Time by saying that it is because of the successive nature of time that one can only be aware of one inner concept at a time. Moreover, Kant draws a distinction between the empirical nature of Space and Time; unlike Space that exists and holds several appearances simultaneously, Time can only have one concept at a time. It, therefore, goes through intervals in order for it to have several different inner concepts or images. Time is also transcendently ideal because it cannot be removed from our mind, and concepts cannot be thought without Time. Kant says, “We cannot, in respect of appearances in general, remove time itself, though we can quite well think time as void of appearances.” This is to say that time is an independent phenomenon that does not require the aid of our sensibilities in anyway. Our sensibilities, on the other hand, are dependent upon Time, and it is the concepts of our inner mind that are dependent upon the time as necessary component for appearances. In other words, humans' inner perception or capacity to imagine is based upon the Time that is a priori to our mind.
