Kant & The Critique of Pure Reason

Immanuel Kant lived in the 18th century and was the founder of German Idealism. He is considered by many to be the greatest modern philosopher. Idealism itself is an old thought going back at least as far as Plato, and can in essence be described as the thought that reality is made up of ideas. Subjective Idealists (such as the Empiricists Berkeley & Hume) say that everyone perceives their own unique and subjective reality. Objective Idealists (such as Plato and Leibniz) say that reality is objective but transcends our perceptions, meaning that humans are incapable of perceiving true reality. Both positions, when taken to extremes, become increasingly implausible. Kant’s version of Idealism was partly an attempt to rebuke both (as well as Romanticism), and provide a definitive version of Idealism. German Idealists such as Hegel, Fichte and Schopenhauer would go on to dominate the 19th century. Today however, Idealism in general has not recovered from the attacks sustained by Russell, among others, in the 20th century.

The Four Categories of Logical Proposition

In order to construct his new Idealism Kant relies on two distinctions, one between ‘analytic’ and ‘synthetic’ propositions, and the other between ‘a priori’ and ‘empirical’ propositions. An analytic proposition is one where the predicate is a part of the subject. For example, ‘a triangle [subject] has three sides [predicate]’. Having three sides is part of the definition of a triangle. All other propositions are synthetic, such as ‘Napoleon [subject] was a great general [predicate]’. It is not inherently part of the definition of ‘Napoleon’ that he was a great general – that is a point of view. An empirical proposition is one that we can only know to be true based on observation (sense-perception). A priori propositions can be known by means other than observation, e.g. by reason. Combining the two distinctions, it can be shown that analytic propositions are always known a priori (this allowed him to disprove the hard-line empiricist position that nothing can be known a priori). As long as you fully understand the concept of a triangle, you will automatically understand that a triangle has three sides, without need for further observation. If analytic propositions are always known a priori, is the opposite true – can synthetic propositions ever be known a priori? For example, can any proposition regarding space and time be known purely by reason and not by experience? The answer to this question forms the basis for Kant’s work ‘The Critique of Pure Reason’.

The Subjectivity of Space & Time

Kant agrees with the Subjective Idealists in saying that objects themselves are unknowable. All we can know are the sensations that objects cause, and these sensations are processed in the mind so are therefore subjective. He also says that the relationship of objects to space and time are subjective.  Space and time are part of our apparatus of perception. Just like wearing blue glasses would cause everything to appear blue, so we experience the world wearing space and time glasses which cause us to experience things in the context of space and time. Because it is our minds that order things in space and time, we each do this a bit differently, such that the experience of space and time is subjective. Kant argues that attempts to understand space and time objectively through logical analysis leads to contradictory propositions which can all apparently be proven. For example, it can be argued that the Universe has a starting point in time and has a certain size, and it can be argued that it is infinite in both space and time. The fact that both contradictory positions can be argued through pure reason means that space and time cannot be understood this way, but rather through subjective experience; hence the critique of pure reason.

Kant argues that our understanding of space and time are known to us a priori (by reason and independent of experience). Starting with the belief that things do not themselves have properties of space and time, Kant argues that the mind must arrange things in space and time, and to do that the mind must understand space and time without need for observation. However, Kant does not explain why the mind positions things in the way it does, and why everyone’s mind appears to position things in the same way. To give Russell’s example, why do we all position eyes above the mouth, and experience thunder after lightning? Russell argues that while it is reasonable to argue that we subjectively perceive qualities of things (through seeing, hearing, feeling etc) but not objective things themselves, and our perceptions may be different to the things themselves, we should say that the two correlate. For example, we see colours rather than the wavelengths that cause the colours, but there is a correlation between them. In that sense space is no different. There is the subjective space which is part of what we perceive, and the objective space which we can only infer. If we subjectively perceive something to be located to the left of something else, that cannot be random, but must correlate in some way to the objective position of those two things. Russell argues that time is different, in that there cannot be subjective time. If we experienced the sequence of events in time subjectively, then even something as simple as having a conversation with someone would be extremely difficult.

The Categorical Imperative

Pure reason can allow us to form new ideas, but cannot prove these ideas to be real. Kant illustrates this point by attacking the proofs for God’s existence, which are based on pure reason (including the ontological argument – Kant simply says that it is possible to imagine something that does not exist). For Kant, the only correct practical use of pure reason is to solve questions of morality. Indeed, reason is the only way to solve questions of morality, and the method for doing so is as follows. Kant defines an imperative as a proposition that declares a certain action to be necessary, and there are two types of imperative. A hypothetical imperative is one that says an action is necessary in order to achieve a particular objective. However, this cannot determine whether the action is right or wrong, because it depends on whether the objective is right or wrong (Utilitarianism is based on a hypothetical imperative, and was therefore rejected by Kant – how do we know that maximising human happiness is the right objective?). A categorical imperative is one that says an action is necessary as an end in itself. Kant determines that there is one overarching categorical imperative; an action is right if it is possible for everyone to do it, and if we would be happy for it to do done to us. Kant’s example is that it is logically impossible for everyone to borrow money, as there would be no money left. Actions such as theft and murder are likewise condemned by the categorical imperative. Kant thereby claimed to have created a new system or morality based purely on reason. Returning to an earlier question from this post, the categorical imperative is a type of synthetic proposition, and one that can be known a priori. In political terms Kant’s morality could be used as a defence of democracy over absolute rule. It is logically impossible for everyone to rule absolutely as there would be no one left for any of us to rule. It is possible for us each to have an equal say in how we are ruled.

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