Immanuel Kant was born during a time of great discovery in the fields of the physical sciences, by the likes of Sir Isaac Newton. These discoveries included Newton’s three laws of motion as well as the explanation of gravity, all of which were discovered via methods which are now referred to as the scientific method. At the time, these methods were known to be used by empiricists, who maintained that the objects of sensation are the only proper objects of knowledge, that all ideas and knowledge are derived from the senses; through reasoning and observation. In contrast to the thoughts of empiricists, another school of thought existed, referred to as continental rationalism. Rationalists argued that some knowledge and ideas were not derived strictly through sensation, but could also be innate to reason. These innate ideas would give knowledge of a greater reality, which would be known without having to be realized by the traditional senses. This was referred to as being the supersensible reality, in which God existed.
As empiricism believed that knowledge was of the sensible reality, that which can be sensed, led to admitting that there is no reality outside of what can be sensed. As such, there could be no immortality of the soul or of the freedom of will; both being unable to be proved through the senses. This proved to have great implications with what is taught through religion, as there is a supersensible reality in religion. Although both rationalists and empiricists were both trying to provide answers to the same epistemological question, what knowledge is and how it is acquired, they had very different perspectives upon the matter.
Kant was an avid scholar, who without question was adept at many different fields of study. Having these different perspectives in hand influenced Kant’s work of a Critique of Pure Reason. This work holds that there are two types of ideas and knowledge, those that are from sense and those that are innate to reason, essentially fusing the schools of thought of empiricists and rationalists. These two types of thought were of a priori knowledge, being innate to reason, and a posterior knowledge, which is gained through reasoning and observation. Furthermore, each of these types of knowledge were of two different worlds, being the noumena and the phenomena. The world of the noumena was the supersensible world, whereas the phenomena was of the sensible world. Kant’s belief was that which is supersensible cannot be proved nor disproved, and so can only be accepted with faith and belief. This idea was different than of rationalists in that rationalist believed that supersensible ideas could be proven through arguments, and not having to appeal to the senses. Kant distinctly separates faith from fact, fusing empirical and rationalist thoughts. Kant’s next work, the Critique of Practical Reason, involves Kant recognizing that there are two key reasons for human conduct, the will and what is desired. What is desired was said to be subject to cause and effect of the sensible, the world of the phenomena. As the will is compromised, as Kant explained, by this causal and effect, the freedom of the will can only belong in the world of the noumena. This presupposition, of the freedom of the will, is the first in this critique. The second of Kant’s presupposition was that the soul is immortal. This is caused by conduct which is not ideal. By what is desired, it would then be impossible to become morally perfect during a lifetime. To become morally perfect, the soul would have to take to the world of the noumena, and there it could strive to its perfection. Thirdly, it was presupposed that there is the existence of God. God is the absolute good that which the soul is striving towards, and it is only God that can allow for happiness that one earns from their morality. In this, Kant explains that the sensible world does not allow for equal amounts of happiness in correspondence to the good that humans do, or are worthy of. This can only be achieved in the supersensible world, just as the two other presuppositions. It is clear that as these arguments for the freedom of the will, immortality of the soul and the existence of God are of the noumena, they cannot be proven or disproven. Therefore, they are not proofs but rather are possible explanations. In the work of Religion Within the Limits of Reason Alone, Kant explains that religion and morality are both one and the same. This is explained through Kant’s earlier works, as he maintains the same presuppositions. As the soul is striving towards becoming morally perfect, God provides examples of moral perfection. Kant explained that Jesus Christ was an example of this moral perfection. For the reason that all mankind strives to have their soul reach moral perfection, this would lead to the unity of all religion, as the end goal to be achieved are all identical. The explanation of the world of the noumena and phenomena was used to explain the epistemology to be used by Kant in his later work, which applied the reasoning into explaining a possibility for the existence of God. The presuppositions made in the work of the Critique of Practical Reason were later used to help determine that all of humanity strive towards the same moral ideal, and thus, all religions are united in ethics and morality.