Through this argument, Kant establishes why being immoral is also being irrational:
"1. If you are rational, then you are consistent .
2. If you are consistent, then you obey the principle of universalizability.
3. If you obey the principle of universalizability, then you act morally .
4. Therefore, if you are rational, then you act morally .
5. Therefore, if you act immorally, then you are irrational."
Because of this, Kant believes that every form of immorality is a form of irrationality, because acting immorally means the agent is making mistaken assumptions and reasoning poorly. Are there examples of irrational behavior that isn't immoral? Schafer-Landau gives us the example of a contracted serial killer who knows what they are doing and the results of their actions. Even though most of us would see him as immoral, can we claim he's irrational?