"In consequence of this revolutionary assertion Kant states that: 'Space is not an empirical concept which has been derived from outer experiences.' (B/38) On the contrary: '…it is the subjective condition of sensibility, under which alone outer intuition is possible for us.' (A/26; B/42)
In other words, Kant asserts that space (and time) are not objective, self-subsisting realities, but subjective requirements of our human sensory-cognitive faculties to which all things must conform. Space and time serve as indispensable tools that arrange and systemize the images of the objects imported by our sensory organs. The raw data supplied by our eyes and ears would be useless if our minds didn't have space and time to make sense of it all. ...
Kant's view of space (and time) is the groundwork of his Critique [of Pure Reason], However the inseparable bond he claimed between geometry and the nature of space serves to undermine his case rather than support it. ...
When Kant refers to geometry, he must mean Euclidean geometry, since Non-Euclidean geometry, the brainchild of the 19th Century, was unknown to him. Hence space, in Kant's philosophical system must conform to Euclidean geometry. Norman Kemp Smith, in his Commentary on the Critique, remarked that for Kant '…space in order to be space at all, must be Euclidean.'
Space, in Euclidean Geometry, is a concept which is independent of the attributes of our human minds and senses. The word Geometry is derived from Greek - geo 'earth', and metron 'to measure', namely 'earth measurement'. With such semantic-conceptual roots its hardly conceivable that Euclid regarded Geometry as divorced from an objective independent space."
(Pinhas Ben-Zvi, 2005, Philosophy Now)
Ben-Zvi, P. (2005). "Kant on Space." Philosophy Now, January/February 2005(49).