Kant’s Moral Argument for God

(This summary was produced for my classes)


Kant’s Moral Argument for the Existence of God

©Peter Sjöstedt-H


–       Immanuel Kant (1724-1804) – the ‘Godfather’ of modern philosophy – is generally revered for his three critical books: The Critique of Pure Reason (1st) , The Critique of Practical Reason (2nd), and the Critique of Judgement (3rd).

–       In the 1st critique, which sets out the conditions for knowledge, he criticises former so-called ‘proofs’ for the existence of God – namely, the ontological and cosmological arguments. In the 3rd critique, he criticises the teleological argument (even considering evolution (prior to Darwin)).

–       Nonetheless, Kant believed in God, though he was critical of church practice.

–       Kant was adamant that God could not be proved in any positive way. Not by reason, nor ‘revelation’ (he wrote a critique of the Christian mystic, Swedenborg). However, he did argue – in the 2nd Critique – that one could assume God existed because morality existed.

  • So, one cannot prove that God exists, but one can assume that he exists through reason.

–       To fully understand Kant’s rather complex argument, one must really understand his whole philosophy, especially his ontology (theory of existence), epistemology (theory of knowledge – which is linked to his ontology), and his ethical theory.



Ethical Theory

–       Kant’s ethical theory is first properly devised in his short book, ‘Groundwork of a Metaphysic of Morals’ (GMM) (1785).

–       Kant is considered a deontologist, which is to say that an action is morally good if its intention, rather than its consequences, was good. So, in some cases, one is being moral even when the consequences are knowingly bad.

  • E.g. Not stealing money to save someone’s life.
  • A consequentialist, like a utilitarian, would consider the opposite – stealing – the moral option.

–       Deon in deontology means duty. For Kant, morality is doing one’s duty,

–       But one’s duty is not dictated by a set of prescribed rules, but is rather dictated by one’s own reason.

–       In GMM, Kant argues that the reason we have reason is not to seek pleasure (as an instinct would suffice for this), but rather therefore to have a good will. [This is very questionable!]

–       Now, subjective principles seek pleasure (e.g. “I would like to earn money for nothing.”) – so a good will must use objective principles. (e.g “I would like everyone to be happy.”)

–       Kant called the most general moral objective principle, the Categorical Imperative, which reads:

  • “Act only according to that maxim [principle] whereby you can at the same time will that it should become a universal law.” (GMM)
  • So, for example, I would not steal because I would not want stealing to become a universal law.

–       Now, as Kant’s morals are based on intentions (objective principles), a problem arises: If everything in the universe is caused by something else, then even the actions I perform are merely determined by prior causes. So what seems to be my intentions are actually only part of a causal chain: determinism.

  • In other words, for (intentional) morality to be possible, we must have free will. We cannot be determined by past causes. Otherwise we cannot say that we even have intentions, they are merely actions and we would be automatons.

–       So, for morality to be possible, free will must exist.

  • “were there no freedom it would be impossible to trace the moral law in ourselves at all.” (2nd Critique, preface)

–       Many philosophers and scientists do not believe in free will because of different types of Determinism. You may be determined to act socially, biologically, even logically: the belief that every effect in the universe must have been caused by something else (causality).

  • Indeed, this is the postulate of the cosmological argument for the existence of God (by, for example Aristotle and Aquinas).
  • Kant rejected that argument for the same reason he rejects the refutation of free will:

–       Kant actually believed in both causality and in free will.

–       He could do this because of his ontology. He divided reality into two: phenomena (appearances) and noumena (things-in-themselves).

–       Causality exists in the phenomenal world – the world of empiricism/natural science. But free will exists in the noumenal world and so intentions are not caused by physical/phenomenal things.



–       Kant brought together two previously opposed strands of philosophy: Empiricism and Rationalism.

–       He argued in the 1st Critique that in order for us to be able to perceive anything in the world, we actually have to impose/project concepts onto the world first.

  • For example, space and time do not exist in the real/noumenal world; rather, they come from our minds and are projected onto ‘reality’ so that we can perceive things in space and time.
  • We do not get our ideas of space and time from experience (a posteriori) therefore. Contrariwise, we get experience from time & space being first projected (a priori).

–       Time & space are thus called ‘pure concepts of the understanding’ and therefore do not really exist (in the noumenal world).

–       Another pure concept of the understanding is causality (logical determinism).

–       I.e. we can only make sense of the world/universe, by projecting causality (cause & effect) upon it – though in (noumenal) reality, causality does not exist.

  • I.e. we have evolved to find a cause for every effect we perceive. In reality, this is an assumption.
  • Causality is necessarily uncertain – therefore it cannot be used to attain a certainty (e.g. God from cosmological argument – Hume’s criticism).
    • If I hit the table, the cause (hitting) produces the effect (a sound). But no matter how many times I do that to prove to you that it is a law of physics, it is never certain because one day it could conceivably not happen (induction). But we assume it does it from our mind as it helps us develop in the world.

–       Kant therefore argues that like space & time, causality is an a priori concept – rather than an actual real law.

–       Causality therefore applies to the phenomenal world, but not to the noumenal world.

–       By making this ontological move, Kant makes (intentional) morality possible:

  • Everything that is determined/caused lies in the phenomenal world, therefore free will lies in the noumenal world where it cannot be caused/determined in any way, as causality does not exist there.
  • The soul (or, the ‘pure apperception’) is also necessarily noumenal as it is the condition for experience and therefore cannot be experienced (i.e. be phenomenal) itself.



–       One later formulation derived from the Categorical Imperative is the Formula of the End in Itself which reads:

  • Act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end. (GMM§2)
  • I.e. never exploit others, including yourself (i.e. respect yourself, do not slave away for others)

–       Therefore, the purpose of reason is not only a morally good will (as stated at the beginning of the GMM), but also the happiness of oneself.

–       The ultimate goal of reason, the highest good, therefore is a combination of virtue and happiness – this Kant calls the summum bonum (Latin for ‘highest good’).

–       But be careful: the summum bonum is not the reason for being moral – it is rather merely the later goal as a result of  being moral.

  • “though the summum bonum may be the whole object of a pure practical reason, i.e., a pure will, yet it is not on that account to be regarded as its determining principle; and the moral law alone must be regarded as the principle on which that and its realization or promotion are aimed at.” (2nd C. Book 2, §1 – p.84)
  • i.e. One is moral because of rational duty (Categorical Imperative); as a result of following this duty one understands that the highest good –summum bonum – is only attained if one is both moral and happy (as one should not exploit oneself according to the formula of the end in itself).

–       So by being moral, one should ideally also be happy. But in many cases, the moral person is exploited and/or never receives his dues.

  • One can be moral but this often results in self-sacrifice, thereby transgressing a part of the moral law: the formula of the end in itself.

–       So, the summum bonum is not often achieved (in this life), which leads Kant to postulate two things: the Immortality of the soul and God.

–       Because morality is based on reason, and morality logically demands the summum bonum, then the fact that it is not achieved in our phenomenal life implies that our soul must live on after phenomenal death so that the summum bonum can later be achieved. Thus morality implies the immortality of the soul:

  • “[the summum bonum] can only be found in a progress in infinitum towards that perfect accordance, and on the principles of pure practical reason it is necessary to assume such a practical progress as the real object of our will. Now, this endless progress is only possible on the supposition of an endless duration of the existence and personality of the same rational being (which is called the immortality of the soul). The summum bonum, then, practically is only possible on the supposition of the immortality of the soul; consequently this immortality, being inseparably connected with the moral law, is a postulate of pure practical reason.” (2nd C – book 2,§1-2 para 35, p.96.)


–       Furthermore, Kant argues that, Happiness is the condition of a rational being in the world with whom everything goes according to his wish and will; it rests, therefore, on the harmony of physical nature with his whole end and likewise with the essential determining principle of his will. (ibid.)

  • I.e. Happiness is when a rational will (i.e. moral will) is in harmony with the whole of nature – I get what I want (which here is moral not merely selfish!).


–       Because reason logically dictates that the summum bonum should be achieved, there must be a cause of the harmony of morality and happiness.

–       This cause cannot lie within nature as it is the cause of nature (our reason and will being part of nature).

–       Therefore the cause must be metaphysical (noumenal).

  • “Accordingly, the existence of a cause of all nature, distinct from nature itself and containing the principle of this connection, namely, of the exact harmony of happiness with morality, is also postulated.” (ibid.)

–       This metaphysical cause is God. Humans cannot be the cause as we are part of nature, and therefore not the cause of nature (reason).

  • Now it was seen to be a duty for us to promote the summum bonum; consequently it is not merely allowable, but it is a necessity connected with duty as a requisite, that we should presuppose the possibility of this summum bonum; and as this is possible only on condition of the existence of God, it inseparably connects the supposition of this with duty; that is, it is morally necessary to assume the existence of God. (ibid.)

–       In sum,  the summum bonum, which is a result of reason, postulates a necessary harmony between being moral and being happy. This harmony may not be achieved in our lifetime which postulates the immortality of the soul. The harmony itself is not only a logical expectation, but a necessary reward for being moral.

–       As the summum bonum is a duty as well as a reward, there must be a God who ensures that this harmony (morality & happiness) is attained. Otherwise, reason would deliver a goal (summum bonum) which was unattainable (which is rationally disharmonious).

–       Therefore morality postulates the existence of God.


–       Kant calls this postulation of God a ‘necessary hypothesis’.

–       It is not knowledge, but assumption. Knowledge requires that understanding be combined with perception – a metaphysical being cannot be perceived by definition.

–       Kant continues by identifying the summum bonum with the Christian notion of the Kingdom of God.

–       So, for Kant, at the end of reason we discover religion. Although religion can never properly be known, in a strict sense. Just assumed to be necessarily true.

–       “In this manner, the moral laws lead through the conception of the summum bonum as the object and final end of pure practical reason to religion, that is, to the recognition of all duties as divine commands, not as sanctions, that is to say, arbitrary ordinances of a foreign and contingent in themselves, but as essential laws of every free will in itself, which, nevertheless, must be regarded as commands of the Supreme Being, because it is only from a morally perfect (holy and good) and at the same time all-powerful will, and consequently only through harmony with this will, that we can hope to attain the summum bonum which the moral law makes it our duty to take as the object of our endeavours.” (2ndC. – book 2,§2, para50, pp.100-101)


–       Note: for Kant, God is not the motive of our morals, but the assumption of our morals:

“…it is morally necessary to assume the existence of God … I also do not mean by this that it is necessary to assume the existence of God as a basis of all obligation as such (for this basis rests, as has been proved sufficiently, solely on the autonomy of reason itself).” (2ndC. book 2, §5)



©Peter Sjöstedt-H

(Note: I believe this argument for God to be seriously flawed!)

immanuel kant deontology god ethics morality categorical imperative