David Hume and Immanuel Kant have both had tremendous impact on the field of philosophy. Their contributions, especially "A treatise of human nature" by Hume and the "Critique of pure reason" by Kant are masterpieces in philosophical literature. Both of them have left their own novel ideas and concepts, which deeply influenced and gave a new understanding to domains as diverse as philosophy, politics and religion. Let us study the ideas of Hume and Kant in a little detail and try to have a comparative study of their philosophies.
Hume's Matters of Fact and Relations of ideas
Hume's analyses of human mentality is based on two different components namely impressions and ideas. Impressions are vivid and strong creations of our experiences while ideas are feeble reflections of the impressions. According to Hume all ideas have a preceding impression. All human belief systems are a result of the linking or the association that we perceive between the different ideas in our mind. Human understanding and his learning process are mostly based on what are called the "matters of fact." Hume proposes that our casual reasoning does not have rational justification. His main contention is that our beliefs in 'matters of facts' do not have any real rationale. He argues that the belief that we import from our past observations hold no guarantee of their certainty in future. As an example Hume states that people believe that the sun will rise every day. This belief has as its origin the firm faith in the relation between the rotation of earth with respect to the sun, which again is based on our experiences in the past. Hume's proposition is that our assumption of the continuity of the 'matters of fact' based on past criterion are not rationally justified. That is to say that Hume considers inductive reasoning as not having a rational basis.
Hume was one of the first philosophers who found out a discrepancy in the assumption that all knowledge a priori must be purely analytical. In particular he found out that the relationship between the 'cause and effect' is purely synthetic rather than analytical. That is, philosophers before Hume were of the opinion that any effect could be correctly deduced or ascertained from the cause provided we have the knowledge. Hume differed here from them in that he dismissed the notion of a priori knowledge pertaining to the connection between the cause and effect. It is necessary to note that Kant's idea of synthetic judgement is in response to Hume's rejection of the possibility of a priori knowledge pertaining to cause and effect.
According to Hume we can never know the relationship between a cause and effect by way of priori knowledge. Continuing in the same vein even 'matters of fact' which we accept based on our memory and our sensory perception cannot be cognized by knowledge a priori. In short, a priori knowledge is possible in case of propositions where the 'contraries create a contradiction'. [David Hume] This implies that matters of facts can only be understood by way of posteriori knowledge. Hume's famous elucidation "the sun will rise' is an excellent example of 'matter of facts' which depend on posteriori knowledge. 'Matters of facts' differ from 'relations of ideas' in that they cannot be deduced from priori knowledge. Relations of ideas are totally discernible propositions and can be proved by way of reasoning. [David Hume]
Kant's Definition of Knowledge
Accumulation of knowledge is a process, which involves sensory input together with innate cognitive response. Kant argues that the operation of this cognitive faculty is very subtle and hence difficult to perceive. Kant identifies two separate forms of knowledge namely priori and posteriori. He defines knowledge, which falls beyond the realm of experience as a priori. What is a priori for a person might just be a posteriori for another person in a different period of time. That is to say that experience garnered by people in the past might just be accepted as priori by the future generation. (Impure priori). On the other hand a pure priori represents knowledge which is bereft of any empirical origins. Therefore 'knowledge a priory' is a combination of both pure priori and impure priori.
The existence of priori
Kant justifies the existence of a priori by the following reasoning. When we allow our logical analysis to continue we find out that empirical knowledge, which is reflective of our experiences, is based on a certain set of rules. Further reasoning makes it clear that these rules upon which we derive our empirical knowledge cannot be totally empirical as then it would imply that the rules do not have a generality and consequently the criteria of their applicability is at a question. In other words a priori is very generalized and universal in nature. Knowledge a 'Priori' exists beyond the realm of the senses.
Analytical and Synthetic judgements
Kant defines any relationship between a subject and a predicate into two different categories namely analytical and synthetic judgements. Analytical judgements are those judgements, which fall within the domain of our conceptions without the need for any support from experience. Analytical judgements are based on a priori because all the conditions that were applied in arriving at the judgement were found within the bounds of conception. Synthetic judgements on the other hand are arrived at by practical assertions. Kant explains this by giving the following explanation. The expression "All bodies are heavy" is a synthetic judgement because it involves more than mere conception to arrive at the judgement. Another example is "a straight line between two points is the shortest." [Immanuel Kant] This is a synthetic judgement in that our conception of the straight line by no way accounts for the 'shortest path'. That is to say that the quality of 'shortest' is outside our conception of the straight line.
So we see that Kant considers the possibility of synthetic judgements a priori in all scientific fields of reason. For example even in pure mathematics the propositions, which we tend to prove, are purely based on our conceptions and do not have any empirical basis. Arithmetic propositions in particular are synthetical rather than analytical. For example even the simple summation of two numbers (7+5 =12) as explained by Kant extends beyond the realm of conception, as we simply cannot conceive of two numbers being contained in a single number. Kant argues that there is an operation of 'objects of intuition' which makes us identify with external objects to aid in our understanding (our fingers used in the counting) thereby automatically implying the synthetical nature of the proposition. The inseparability of the intuition in our understanding of these mathematical propositions explains that mathematical propositions are synthetical judgements, which depend on the faculty of intuition alongside our conceptionable ability.
Kant extends his synthetical a priori judgements to material physics. He elucidates this by using a simple proposition, "In all changes of the material world, the quantity of matter remains unchanged." In the above statement is a priori but the fact that it discusses the permanency of material objects falls beyond our realm of conception of matter. That is to say that the issue of 'permanency of matter' seems to be an entirely new aspect, which is separate from our conception of matter. Since the above proposition extends our thought beyond our stream of conception it is a synthetical priori and not a purely analytical one. [Immanuel Kant]
We can correlate Kant's analytical judgements to Hume's relations of ideas. Both of these concepts are similar in that they do not require the realm of experience to understand them. That is both "analytical judgement" and "realm of ideas" are concepts that are based on a priori knowledge. However Hume and Kant differ considerably in their ideas of "matter…