"The universe is full of magical things patiently waiting for our wits to grow sharper."-- Eden Phillpotts
"In truth, truth inhabits fiction as the master of the house."--Jacques Derrida
"The world is governed more by appearances than realities, so that it is fully as necessary to seem to know something as to know it."--Daniel Webster
"Hell is truth seen too late."--Thomas Hobbes
Hume and Kant
Alice C. Linsley
David Hume categorized all objects of human reason into two groups: Relation of Ideas and Matters of Fact. This is often referred to as "Hume's fork" and can be further investigated in An Enquiry Concerning Human Understanding, Section IV, Part 1. Here we read: "All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas and Matters of fact. Of the first kind are the sciences of Geometry, Algebra, and Arithmetic... discoverable by the mere operation of thought... Matters of fact, which are the second object of human reason, are not ascertained in the same manner; nor is our evidence of their truth, however great, of a like nature with the foregoing."
The truth claims that Descartes posed when he introduced the evil deceiver argument are in Hume's second category - "relations of ideas" and Descartes further developed the argument that all real knowledge consists of relations of ideas, including knowledge of the material world. Descartes thought that the material world can be explained by physical laws of causation and that one day physics would be established as an a priori science along with geometry and algebra. Hume, on the other hand, sought to demonstrate that science is not a priori. Instead, Hume argued that there is never certainty concerning causes and effects by using reason alone. Science requires experimentation and observation, and there is always the possibility that the next experiment might not provide the same results or conform to the hypothesis as did earlier experiments.
This radical doubt poses a problem for scientists. It means that the scientific method cannot be said to ascertain beyond doubt. This is Hume's problem of induction. Inductive methods predict or infer and are essential in scientific reasoning. One cannot assume that something is immutable and necessary because it has always or usually been reliable in the past. Though 20 experiments produce the same results, we have no certainty that the results will be the same after experiments 21, or 32 or 45. Though the sun has risen daily since the founding of our solar system, we have no certainty that it will always do so.
In 1953, Richard Rudner published “The Scientist qua Scientist Makes Value Judgments,” in which he argued that since no hypothesis is ever completely verified, in accepting a hypothesis the scientist must make the decision that the evidence is sufficiently strong to warrant the acceptance of the hypothesis. The problem of induction which David Hume framed so precisely is really a problem of decision about which action to take, not proof of the fallibility of science in general. For Hume this is where the element of the human imagination comes in to play. In Hume's view the most ordinary interactions and common observations of bare facts involve active imagination. They do not represent passive perceptions of the world. His critique of metaphysics involves a criticism of what he sees as lack of imagination or blind imagination. In his view, the errors of philosophy arose from the fact that imagination determined human thought more than people recognize.
Immanuel Kant (1724-1804) was aroused from his "dogmatic slumbers" by David Hume. Kant thought that Hume went too far in his skepticism about the capability of the inductive method of science. He saw greater agreement among scientists than among philosophers and thought that, unlike metaphysics, the motions of material objects are governed by laws. Everything that happens is determined by antecedent happenings or prior conditions. But this caused a problem for Kant's anthropology. If everything is predetermined in the universe, how is it that humans have free will?
Kant concludes that the human has free will to choose to fulfill his duty at any given moment and the universal moral law concerns performance of duty, regarding humanity as an end in itself rather than as something to be used to achieve selfish ends.
Critique of Pure Reason, Kant agrees with Hume that there is no absolute ground to assume the existence of God. However, against Hume, he adds that the idea of God is intrinsically connected to happiness and morality as the “ideal of the supreme good.” In his later treatment on Logic (1800), Kant argues that the idea of God is proved only through the moral law and only with “the intent so as to act as if there be a God.”
I say that every prince ought to desire to be considered clement and not cruel. Nevertheless he ought to take care not to misuse this clemency. Cesare Borgia was considered cruel; notwithstanding, his cruelty reconciled the Romagna, unified it, and restored it to peace and loyalty. And if this be rightly considered, he will be seen to have been much more merciful than the Florentine people, who, to avoid a reputation for cruelty, permitted Pistoia to be destroyed. Therefore a prince, so long as he keeps his subjects united and loyal, ought not to mind the reproach of cruelty; because with a few examples he will be more merciful than those who, through too much mercy, allow disorders to arise, from which follow murders or robberies; for these are wont to injure the whole people, whilst those executions which originate with a prince offend the individual only.
It is possible to argue with Machiavelli that reason might lead to actions that in most contexts are regarded as immoral.
Kant's synthetic a priori knowledge
One of Kant's contributions is in the area of logic. He recognized a class of propositions termed "synthetic a priori." Such propositions are distinct from a posteriori judgments based on observation and experimentation. These judgments, being of an empirical nature, are largely descriptive; that is they define rather than inform. In this class of propositions we find propositions such as "a bachelor is an unmarried man" or "swans are waterfowl." A synthetic judgment, informs, not merely defines. Typically, synthetic judgments are associated with a posteriori knowledge (knowing the particulars) and analytic judgments are associated with a priori knowledge (knowing the universals). An example of a synthetic a posteriori judgment is “all swans are white.” This is synthetic because whiteness is not a necessary part of the concept of swan. The statement is also an example of an a posteriori proposition because the only way to find out if all swans are white is from observation and experience.
Kant argues that mathematics and the laws of physics contain synthetic a priori knowledge. For example, “7 + 5 = 12” is a priori because it is a necessary and universal truth we know independent of experience, and it is synthetic because the concept of “12” is not contained in the concept of “7 + 5.” Kant argues that the same is true for the laws of physics such as “for every action there is an equal an opposite reaction.” Because such laws apply universally, they must be a priori knowledge, since a posteriori knowledge only tells us about particular experiences. The fact that we are capable of synthetic a priori knowledge suggests that pure reason is capable of knowing metaphysical truths.
Kant suggests something very like Hume's understanding of the mind. Much of what we consider to be reality is shaped by perception. Kant agrees with Hume that the mind does not passively receive information provided by the senses. Rather, it actively shapes and makes sense of that information. If all the events in our experience seem to take place in a temporal progression, that is our minds arrangement of sensory experience. If we perceive that some events appear to cause other events, that is because our mind's cause-effect arrangement of events. According to Kant, the mind is constrained to perceive or experience sensations in time and space and according the laws of causation. He argues that time and space are intuitions of our faculty to sense things, and physical laws such as gravity and inertia are intuitions of our faculty to understand things.
Related reading: Theories of Knowledge - Part 1; Theories of Knowledge - Part 2; Theories of Knowledge - Part 3; Why David Hume Was Wrong: Immanuel Kant, What is Enlightenment?