The three postulates

Immortality

• Kant states that "the belief in God and another world is so interwoven with my moral sentiment."
• Good people who live moral lives according to duty and goodwill should be rewarded with ultimate happiness.
• Kant proposes that this ultimate happiness or "summum bonum" must exist in the afterlife where justice is served.
• Kant looks for a perfect future where everyone lives in a kingdom of ends.
• The postulate of immortality is that the belief in immortality has to be based on moral disposition and not one hope of future rewards.
• Kant bases his first argument for immortality. As 'nothing is purposeless' each organ into the world has its own specific claim that human life as a whole is an end not in this life but in a future life.
• One person may act in a way that causes them to sacrifice themselves for others, acts like this are still meaningful due to the immortality of humans. God If afterlife exists so must God to enforce this.

God

• We must assume God exists as there is goodness in the world and God is the source of Goodness.
• God was demanded if the goal of morality was to be realized. This does not mean that we follow our duty to please God as duty itself has its own reward but God makes it possible.

Freedom

• In order to make a moral decision, we must have the freedom to choose how we act.
• If we were forced to act in a certain way, we would not really be choosing to act morally or immorally, we would just be acting in the way that we are forced to.
• We are responsible for following or not following our duty, we have the choice.
• Autonomy of the will is vital for Kant.

Strength of using the postulates to make moral decisions

• Kant is hopeful that doing your duty will lead to the realization of the highest good, and that God will ensure that this happens. This is helpful as it will motivate people to do the right thing.

Weakness' of using the postulates to make moral decisions

• Humanists would argue that good people will do good things, simply because they see the value in doing so without expecting any reward in return. Kant's postulate of immortality (and subsequently, God) is not necessary.
• Many people in the world live in repressive regimes and do not have the freedom to make their own moral decisions. Kant is wrong to assume that everyone is free to make moral choices.
• Some philosophers believe that Kant's being in favour of freedom and saying that moral agents must obey the principles given in the Categorical imperative contradict each other, I am free as long as I obey these laws.