Immanuel Kant

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Immanuel Kant (22 April 1724 – 12 February 1804) was a German philosopher who is considered a central figure in modern philosophy. Kan revolutionized classical apriorism and empiricism during the Age of Enlightenment. His contributions towards metaphysics, epistemology, and ethics inspired much of our contemporary philosophy, and helped guide our epistemological discourse away from classical empiricism and rationalism.1 In his Critique of Pure Reason, Kant makes several key distinctions and introduces new terminology that would ultimately revolutionise the way modern philosophers view the epistemological nature of the world.

Historical Context

Born in 18th century Europe, Kant was thrown into a time where the emergence of Newtonian science sparked a social and cultural revolution – The Enlightenment. With his revolutionary discoveries, Newton inspired the society to challenge the norm of Roman Catholicism and evoked an intellectual epiphany where people began to attempt explaining nature without consulting religion.2 As a result, two epistemological schools of thought surfaced: classical rationalism and classical empiricism. The dispute between these two views dominated the 17th century, where rationalists such as René Descartes (1596-1650) and Gottfried Leibniz (1646-1716) and empiricists such as John Locke (1632-1704) and David Hume (1711-1776) were in a stalemate with regards to the epistemological nature of the world.3 Rationalism, or apriorism, is the view that it is possible to attain knowledge independent of experience, i.e. there exists “a priori” innate knowledge that we know as part of our rational nature or through our intuition.4 It holds that through the attainment of synthetic a priori knowledge outside of our sensory experience, we can deduce further theories from those axioms that will allow us to make sense of the world – that is, we are able to rationalise nature without necessarily consulting our senses. Two of its most well known proponents, Gottfried Leibniz and René Descartes, both believed that since: a) senses were unable to provide us with the ‘truth’ due to an irreconcilable level of uncertainty with our perceptions, and b) the world is intelligible and understandable, innate universal knowledge must exist.3 Indeed, retrospectively we now know their respective a priori axioms were unsound, but their theories nonetheless provided more insight on the epistemological issues that both empiricism and itself shared, which will soon be explained. Empiricism, on the other hand, holds the opposite view that only our senses provide us with an accurate description of the world, and only through sensory experiences are we able to capture the objective world that we live in, make sense of each individual observation and of the world through inductive logic.3 Empiricists such as Locke believed that empiricism is superior to rationalism for two distinct reasons. Firstly, Locke argued that classical rationalists often retreated to non-factual (i.e. non-empirical) claims for support: namely intuition and ‘innate’ knowledge. Secondly, empiricist arguments were preferred for their simplicity. However, despite this divide, empiricism and rationalism both suffered from the same 2 criticisms that are proposed by skeptics such as David Hume (1711-1776) and Pyrrho (360-270BC) who brought up the problems of induction and sensations respectively.

A brief summary of these problems, which is needed as Kant offers an ingenious solution to the criticisms that both the empiricists and rationalists faced, is as follows. The ‘Problem of Sensations’ stems from Pyrrho’s skepticism about the reliability of our senses and whether they are adequate in providing us with the “truth”, due to the possibility that reality is not what it seems. This is important because it implies that we cannot ever make claims of truth (or lie) about the world solely based on our observations,5p. 11 thus directly dismantling classical empiricism. Secondly, Hume’s ‘Problem of Induction’ stipulates that it is impossible to attain a rationally certain synthetic statement from a collection of individual observations through inductive logic, no matter how large the sample size.6p. 275 This is because one refuting instance is enough to dismantle the whole generalisation, and that a refuting instance is always possible with a synthetic statement. Together they imply that it is impossible to make objective statements of the world through empiricism. For example, empiricists have attempted to answer the problem of induction by appealing to past occurrences, but this simply results in a circular argument. Likewise, the rationalist axiomatic system was equally unable to provide an adequate solution to these problems. Leibniz attempted to formulate a principle that aims to show the necessity of the “uniformity of nature”. Named “The Principle of Sufficient Reason”, Leibniz states that it is irrational for something to happen – and conversely, for something not to happen – without reason and establishes this as an a priori axiom that any rationalisation of nature must be contingent upon.7p. 62 However, Hume’s problem persists, as this axiom is still inevitably synthetic and simply cannot guarantee the certainty of inductively obtained conclusions.

Major Contributions

Kant, in his first Critique, responds to both these problems, along with revitalising Leibniz’s Principle of Sufficient Reason (hereafter referred to as PSR) in light of its criticism. He aimed to reconcile rationalism with empiricism by devising a system that validated our sensations as means to rationalise nature, whilst also reformulating the PSR based on his ideas of intellect being the preconditions of our experience, resolving both the aforementioned problems. Kant develops the rationalist stance by asserting that there are fundamental synthetic a priori statements that are not only independent of experience, but actually precedes sensation as a precondition that sensory experience is contingent upon. He coined a few terms, as previously mentioned, that aided the articulation of his overall case. To address Pyrrho’s problem of sensations, Kant developed the noumena/phenomena distinction, and asserted that our senses only explained the world of phenomena rather than make objective claims about the world of noumena. Thus, Pyrrho’s problem is irrelevant because Kant simply doesn’t assert that our empirical statements refer to the objective ‘truth’. This distinction divides the world of forms (the “intelligible world”) with the world of appearances (the “sensible world”).8 The former, which he calls the noumena, is the objective reality: a reality representing objects “in themselves” behind our perceptions. To Kant, the world of noumena merely puts up a façade of appearances to the senses,8p. 356 and what we perceive collectively form the world of phenomena.8p. 177 Since our perceptions pertain only to our subjective world of phenomena, Pyrrho’s skepticism regarding the certainty of synthetic statements is avoided – or rather, simply tacitly accepted by Kant, as the Kantian system now simply states that all observational statements don’t make objective claims.

To tackle Hume’s problem of induction, Kant first asserted that there were synthetic a priori forms that preceded experience. Those are: space, time, conservation of substance, and causality. Kant believed he deduced those 4 forms based on 3 premises: Classical empiricism/rationalism does not guarantee absolute certainty, and absolute certainty does exist in the form of Newtonian physics. The former 2 are the forms of sensibility – the transcendental aesthetic,9p. 13 and they are a priori as their existences are independent of any properties, objects or subjective conditions.8p. 177 Space is simply the collection of all external appearances; an intuition that rationalises our reception of the outer world. Time, on the other hand, is the formal a priori condition that governs all appearances by relating it to the agents “inner state”.8p. 180 The latter 2 are forms of pure reason – the transcendental dialectic.9p. 15 Wanting to confirm and extend the validity and success of Newtonian mechanics, Kant aimed to deduce the certainty of causality and conservation of substance by postulating that they must be preconditions of experience, and that the world must follow strict causality, or else the world wouldn’t be knowable.10p. 180 The “totality” of objects is the unity of the limitations the object has in reality, the causal relationships it participates in with other objects, and its necessary existence implied simply by the possibility of its existence.8p. 212 All three aspects form the totality of an object, and collectively the totality of nature.10p. 167 With these concepts in mind, he developed what was essentially Leibniz’s PSR as the Principle of Universal Causation – which necessitates that the principle of universal causality be a priori. If it’s not a priori, our perceptions will be insignificant and baseless in an unorderly world, and it simply directly contradicts the contemporary successes with rationalising the world through mathematical and mechanistic laws, as well as the notion of totality within nature.

Furthermore, with these 4 a priori forms of experience Kant restored the belief that valid synthetic a priori statements may exist, after the setbacks of Descartes and Leibniz. None of these a priori forms are analytic intuitions, as they are not simply a clarification of definitions. Nor are these forms a posteriori, as they precondition experience. Kant provided an incredibly complex yet ingenious way of viewing reality, and his epistemological distinctions of statements as well as the metaphysical distinction of objective and subjective realities has influenced discussions up until the 20th century.

Analytic/Synthetic distinction

Kant also most notably distinguishes analytic statements and synthetic statements in Critique of Pure Reason . His definition of an analytic statement is as such: in a statement containing subject A and predicate B, if the definition of predicate B belongs to the concept of subject A, such that subject A contains the whole definition of predicate B, then this statement is analytic. A synthetic statement, on the contrary, is when the predicate B is not contained within the concept of subject A. He realised that for analytic statements, the concept of the subject is further explicated and analysed by the concept of the predicate, but no new concept is added.8p. 141 On the other hand, synthetic statements are called “judgments of amplification” as the concept of the predicate adds onto the concept of the subject. An example of an analytic statement would be: “All bachelors are single”, where the concept of “being single” is simply a further explication of the concept of a “bachelor”, which is just a single male. An example of a synthetic statement would be: “All flowers are red”. The concept of “flower” does not contain the condition “red”, and thus the predicate “red” adds onto the concept of “flower” to amplify the concept of the subject. All statements regarding experiences are synthetic,8p. 142 for no analytic statement requires extraneous factors outside of the concepts in its formulation.

By defining analytic and synthetic statements and the worlds of noumena and phenomena, Kant has driven epistemological discourse regarding natural sciences into a new era, where the dispute began to circulate around the epistemological nature of synthetic statements in particular and how crucial it is for the notion of testability.11p. 176 To this day, Kantian influences can be seen in much of modern philosophy of science, such as in the theories of logical empiricism, Karl Popper, Thomas Kuhn and more.


One of the main criticisms Kant received was targeted towards the premises he used for the deduction of the Principle. To recall, the premises were: Absolute certainty exists, and a world with no strict causal relationships is unknowable. For the first premise, fallibilists dismantled the view that absolute certainty in science exists after the acceptance of Einstein’s theory of general relativity which replaced Newtonian mechanics. Fallibilism was further exemplified with the acceptance of quantum mechanics along with general relativity by the scientific community despite the irreconcilable contradictions that arise when examining extreme conditions, which illustrated that the scientific community itself does not operate by assuming absolute certainty.

Another criticism of Kant was again, targeted at one of the premises of the Principle. Kant held a strict determinist perspective when devising his Principle, and in light of more recent advances in quantum theory, we know that a certain cause does not necessarily yield a certain outcome. Using the example of a radioactive molecule and its half life, we know that by the definition of “half life” being “the time period where the probability of a radioactive atom decays is 50%”, and as such the atom may or may not decay at a specific time (i.e. at the exact half life value) but rather any time within that timeframe.

A third criticism was presented by A.J. Ayer (1910-1989),12 where he criticised Kant for conflating the psychological and epistemological criteria of evaluating analytic/synthetic statements. In the example Kant gives of “7+5=12” being a synthetic statement, and “all bodies are extended” being an analytic statement, Kant employs 2 different criterion and equates the two without clarification. In the first statement, Kant deems it synthetic as the definitions of “7” and “5” are not contained in “12”. On the other hand, Kant evaluates “all bodies are extended” as analytic simply because it would be contradictory if otherwise. However, a person with knowledge of the symbol “+” would understand that when put together, “7+5” does indeed share the same concept as “12”, and this statement would be analytic if evaluated as the second statement has been.

Furthermore, Ayer amongst other philosophers have shown that Kant was incorrect in assuming Euclidean geometry was a priori and held factual content about physical space i.e. is synthetic,12 as the discovery of non-Euclidean geometry and application by Einstein in his general theory of relativity disproved of this entirely. Consequently, philosophers now see that axioms of geometry do not “hold factual content”, but are merely definitions. This criticism directly dismantles Kant’s a priori form of space as a necessary precondition for rationalising the world.


Here are the works of Kant included in the bibliographic records of this encyclopedia:

  • Kant (2007): Kant, Immanuel. (2007) Critique of Pure Reason. London: Penguin.
  • Kant (1781): Kant, Immanuel. (1781) Critique of Pure Reason. Cambridge University Press.

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  1. ^  Rohlf, Michael. (2016) Immanuel Kant. In Zalta (Ed.) (2016). Retrieved from
  2. ^  Bristow, William. (2011) Enlightenment. In Zalta (Ed.) (2016). Retrieved from
  3. a b c  Samet, Jerry. (2008) The Historical Controversies Surrounding Innateness. In Zalta (Ed.) (2016). Retrieved from
  4. ^  Markie, Peter. (2015) Rationalism vs. Empiricism. In Zalta (Ed.) (2016). Retrieved from
  5. ^  Annas, Julia and Barnes, Jonathan. (Eds.). (1985) The Modes of Scepticism: Ancient Texts and Modern Interpretations. Cambridge University Press.
  6. ^  White, Roger. (2015) The Problem of the Problem of Induction. Episteme 12 (2), 275-290.
  7. ^  Belot, Gordon. (2001) The Principle of Sufficient Reason. Journal of Philosophy 97, 55-74.
  8. a b c d e f g h  Kant, Immanuel. (1781) Critique of Pure Reason. Cambridge University Press.
  9. a b  Guyer, Paul. (Ed.). (1992) The Cambridge Companion to Kant. Cambridge University Press.
  10. a b  Friedman, Michael. (1992) Causal Laws and Natural Science. In Guyer (Ed.) (1992), 161-199.
  11. ^  Friedman, Michael. (2002) Kant, Kuhn and the Rationality of Science. Philosophy of Science 69 (2), 171-190.
  12. a b  Ayer, Alfred Jules. (1952) Language, Truth and Logic. Dover Publications.