Summary – Kant’s moral argument


by Joseph Lynch

Immanuel Kant argues that morality requires belief in the existence of God, a priori. In essence Kant assumes the existence of God in order to solve a contradiction or paradox. Kant claims that human reason faces contradiction unless it believes in the existence of God.

 “There are in the idea of reason obligations which are completely valid, but which in their application to ourselves would be lacking in all reality, unless we make the assumption that there exists a supreme being to give effect and confirmation to the practical laws.” (Groundwork A 589/B 617) Kant

Practical reason is committed as a matter of strict duty to realize the goal of moral perfection. It is also committed as a requirement ofconsistency in rational choice to seek the maximum satisfaction of its given ends. If there is no moral order in the world then it cannot pursue both of these commitments together. The only way to guarantee justice and moral perfection is to assume the existence of God.

So Kant’s conclusion is also an assumption (or what he calls a postulate): moral order is only possible if we assume God as its source.


A. Kant’s Moral Theory

1. Morality is based on the rational will, not on inclination.
2. The Categorical Imperative:
a. Act in such a way that the maxim of your action could be willed as a universal law.

b. Act in such a way so that you treat persons as rational ends to themselves, never merely as means to an end.

3. Morality is not about being happy, but rather about being worthy of happiness. This is only achieved by doing my duty by obeying the categorical imperative. The virtue of dutifulness is at the heart of Kant’s moral argument: an action is moral only if it is done out of duty, not out of sympathy, pleasure or a desire for personal happiness.

B. The Summum Bonum (the highest possible good) is a rational end

1.  Highest good is a combination of virtue and happiness.
2.  Problem: these are logically independent of one another, and self-contradictory – I can’t pursue duty and happiness together (for example, saving a drowning child may be my duty, but the prospect of drowning myself means I could rationally choose not to jump in).

C. Postulates (assumptions) of Morality

1.       Immortality of the Soul: fulfilling the summum bonum is not possible in this life alone.
2.       Freedom of the Soul: we must autonomously promote the summum bonum by freely choosing to obey the categorical imeprative.
3.       The existence of God: only God could establish the summum bonum.

D.      Note: Kant does not claim that the Moral Argument constitutes a proof for God’s existence

He holds that the idea of God, like the idea of freedom, is an inevitable idea of practical reason. Thus, properly speaking, there is no knowledge of God (such an unconditioned reality is not a possible object of experience), but on Kant’s view, this is why God is an object of faith.

E.      Structure of the Argument

Part I

1.      We are morally obliged to perfectly conform our lives to the moral law.
2.      A person isn’t morally obliged to do something he or she can’t do. “Ought implies can.”
3.      Moral perfection must then be possible. [1 and 2]
4.      Moral perfection is not possible in this life.
5.      The moral self must survive death (so that the self can endlessly progress toward moral perfection). [3, 4]

Part II

1.      The moral self must survive death [conclusion of Part I].
2.      The moral self can survive death only if God exists.
3.      Therefore God exists.Note: Kant also emphasizes the issue of happiness and being worthy of happiness. Even if immortality were somehow possible without God, a perfectly just God would still be necessary to ensure that happiness is commensurate with moral worth.


A.      The postulate of God is neither objective nor necessary as a basis of duty: the moral law is given by pure practical reason alone.

B.      If God and eternal life play a deliberative role in moral reasoning, morality collapses into prudence.

C.      At most, Kant might claim that the summum bonum is a possibility not an actual fact. But it need not even be possible in order to be promoted.

D.      Practical judgments cannot establish what the facts are. Consider the following syllogisms: [i] Don’t eat animal fats; butter is an animal fat; so don’t eat butter. [ii] Don’t eat animal fats; it’s ok to eat butter; so, butter is not an animal fat. The conclusions, both logical, are contradictory – one is based on the premise that butter is an animal fat, the second, produces a conclusion that butter is not an animal fat.


A.      A Humanistic morality might well demand promoting the general welfare. But situations might arise in which the general welfare requires the sacrifice of one’s own life. But from a Humanistic perspective, such acts of self-sacrifice are strictly irrational. The rationality of such actions are apparent only in the context of faith.

B.      Criticism: This argument assumes that rationality = self interest. Also, one might contend that extreme self-sacrifice can never be morally obligatory.



Kant’s argument is a syllogism or logical construction that depends on the strength of the premises.
Premise 1: There is a moral order, is disputable – it implies an objective order which we cannot prove.
Premise 2: Human beings rationally pursue the summum bonum is disputable. Morality may simply be a form of self-interest (it may be in my interest to help you).
Premise 3: People want their own happiness, but Kant defines happiness in a strange way as “the state of a rational being in the world in the whole of whose existence everything goes according to his wish and will”. The utilitarian view that happiness is about maximising pleasure and minimising pain is a very different definition.
J Hare has argued “If we are to endorse wholeheartedly the long-term shape of our lives, we have to see this shape as consistent with our happiness” (Hare 1996, 88). This contradicts the first element of Kant’s argument, that duty alone creates moral worth. For example, it may be my duty to join the French Resistance even if the probability of my dying makes me miserable.
But then, Kant’s moral argument was an attempt to solve a contradiction between virtue and happiness.

Korsgaard, C, 1996, The Sources of Normativity, New York: Cambridge University Press.
Hare, J, 1996, The Moral Gap, Oxford: Clarendon Press.







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