Critic der reinen Vernunft

Immanuel Kant (1724-1804) was a German philosopher of the 18th century and a prominent figure in the Enlightenment. Kant's  philosophical work, particularly outlined in "Kritik der reinen Vernunft" ("Critique of Pure Reason") published in 1781, addresses the nature of human knowledge, metaphysics, and the limits of reason.  In this book, Kant seeks to reconcile empiricism and rationalism by proposing that knowledge arises from both sensory experience and innate cognitive structures. Kant introduces the concept of synthetic a priori knowledge, arguing that certain truths are both necessary and informative, not derived from experience alone.

In brief, Kant distinguishes between phenomena (appearances) and noumena (things-in-themselves), asserting that our knowledge is limited to the former.  From the point of Einstein's special theory of relativity, noumena (things-in-themselves) are physical quantities, events et cetera as measured by the co-moving observer (i.e. proper time, rest-engergy et cetera) while phenomena (appearances) are physical quantities, events et cetera as measured by the stationary observer (i.e. relativistic energy et cetera). 

In "Kritik der reinen Vernunft", Kant elaborates on the conditions under which human cognition can make meaningful claims about the world from Kant's own, subjective point of view. However, there are authors who are characterizing Immanuel Kant as a typical agnostic (see p. 235 of this book).

Info:

Y 1790 Kant Immanuel Critic der reinen Vernunft, Third Edition: original work

p. 232 ff: Kants theory of causality

p. 235: Agnosticism

(C) e-rara, zürich, suisse. https://doi.org/10.3931/e-rara-24939