Kant did NOT put forward a moral argument for God's existence as a free-standing argument like the Teleological Argument. Instead, his moral argument is part of his ethical theory.
For Kant, the existence of God is not something we can know through the powers of reason: God's existence is beyond the grasp of the five senses.
We should 'deny knowledge, in order to make room for faith'. The Critique of Pure Reason
Kant thought that God was a postulate of practical reason.
The Moral Law within us
'Good will shines forth like a precious jewel'.
There is universal agreement that some actions are inherently right or wrong. This shows the existence of an objective moral law that everybody is aware of.
Not only are we aware of it but we feel an obligation to follow it because it's the right thing to do (a deontological argument).
However an action is only a matter of morality if this action is one that has been freely chosen - autonomous.
Duty and Summum Bonum
Kant concludes that you should do an action because it is good to do, not because of any consequences such as making you happy, getting a result and so on.
Kant also adds that by doing this achieves the 'Summum Bonum' (highest good). The Summum Bonum is the achievement of moral goodness (virtue) and happiness together.
However whilst we can carry out a virtuous action, there is no guarantee that it will always lead to happiness. Yet it's logical for a virtuous action to be rewarded by happiness eventually.
Kant reasoned that because the Summum Bonum is rarely achieved in a lifetime, logically there must be an afterlife in which to achieve it.
Summary of The Moral Argument
It is logical for perfect virtue to be rewarded by perfect happiness.
Humans cannot achieve the Summum Bonum without God and an afterlife.
God's existence is the guarantee that that ultimately moral virtue and goodness go together and are achievable.
Sigmund Freud (1856-1939) introduced the idea that our behaviour is influenced by psychological causes and not by any divine intervention.
He accepted that we have a conscience but disagreed that it came from God. In Freud's view, our conscience is a product of our unconscious mind, which he called our superego. The superego knows what we should or shouldn't do.
As a baby develops, it gradually gains a sense of self-awareness and its own identitiy, which he termed our ego.
Freud sees the superego as existing independently of our basic wants and desires and sometimes at odds with rational thought. Acting in accordance with the superego makes us feel virtuous.
Freud's Challenges (cont'd.)
Additionally, Freud argued that religion is an obsessional neurosis. It provides a way for people to satisfy their desires, such as that the world would be ordered and life be meaningful.
The answers religion give are appealing, such as the rewards in heaven. Therefore although the Summum Bonum being achievable is a very persuasive human desire, this in no way makes it, or God, a reality.
If Freud is correct, then Kant's claim that morality is objective and discovered through reason is vulnerable. Freud would argue that morality is the product of society and upbringing, and not something to be desired. Thus, if this is true, Kant's argument for God's existence as a postulate of pure practical reason fails.