The most influential answer to the question of principle-based ethics comes from the towering philosophical figure of the 19th century: Immanuel Kant. He laid out the framework for an ethical theory arguing that all the answers to ethical questions can be found in principles determined by practical reason. Practical reason gives rise to the famous categorical imperative, which is an ethical principle that has fascinated and frustrated many students of ethics.

So if you’re trying to get a firmer grasp on the ethics of principle, you’ve come to the right place. Even if you already have a basic understanding of ethics of principle, this lesson can help clear the sometimes muddy waters.

Some people can’t help but think of ethics as essentially about the consequences of one’s actions. According to these folks, if you do something that people generally consider wrong, but it doesn’t make anyone (including you!) unhappy, what’s the big deal? In fact, if your action doesn’t harm anyone, why is it even seen as wrong? This way of thinking about ethics ignores something pretty important, though: principles. Living by principles that spring from your rational nature is a powerful way to live an ethical life.

The following sections start you on laying out what is, for principle-oriented people, the most important ethical theory ever: Kantian ethics. We clarify what principles are and then draw a separation between principles and rules. From there, you see how Kant connects the importance of principles to the faculty of reason and examine how reason itself is seen as important due to its connection to another cool capacity — freedom.

No doubt you probably have a couple of principles that you strive to live by. Everyone does. But what are principles and how do they work? Think of principles as laws that you apply to yourself. They’re those things inside of you that you take so seriously that acting otherwise would be a big deal.

Think of yourself as a mini-government composed of one person. Much like a government, you can decide on laws to follow, such as “I will not steal, even if I think I won’t get caught” or “I won’t break my promises, even if I no longer like the person I made them to.” Like a law made in a government, then, you see it as something that you can’t violate — even in cases where you feel like things would work out better. In fact, make a principle for yourself right now. Go ahead. Stand up and declare something like “I will no longer eat cookies in bed!” Of course, declaring a principle is a little easier than actually living by it. But in order to live by it, you first have to make it yours.

• Which principles are actually worth living by? This is the most important ethical question to ask. There are an awful lot of choices on the menu, and not all of them are ethically acceptable. Kant’s ethics is about which principles are the best ones.
• How many principles does one need? As you’ll soon see, Kant believes that only one extremely important principle exists: the categorical imperative. Having a small number of foundation principles can be better than having lots of different principles, because principles can come into conflict with one another.

Kant’s ethics is based on principles, but principles are very different from rules. Thus, in order to understand his ethical thought, you need to know how they differ. The following comparison shows you the most important differences:

• Rules: Essentially rules are a set of guidelines imposed on you by external authorities, such as God, priests, governments, parents, or even your ethics professor. Many people in the Judeo-Christian tradition get their first exposure to ethical rules through the Ten Commandments of the Old Testament. Most people think of the Ten Commandments as ten rules to live by. If you break any of the commandments (and you aren’t forgiven by God), the usual story is that you go to hell, lose a goat, or experience some other nasty punishment for your transgression. Whatever the punishment, the key point is that God is the enforcer of those rules. According to the book of Genesis, they’re God’s rules for all of humanity.
• Principles: As we note in the preceding section, principles are laws you apply to yourself. So the Ten Commandments aren’t principles all by themselves, because you may not have chosen to adopt them for yourself. Rather, principles are laws that you personally embrace and commit to following, which is significantly different from following a law so you don’t go to hell.

To figure out whether you’re following a rule or a principle, ask yourself why you’re following it. If you’re following it because you fear punishment or want a reward, it’s a rule. If you’re following it because you choose to make it part of yourself, it’s a principle. For example, not speeding because you don’t want to be caught and get a ticket: rule. Not speeding because you aren’t the kind of person who speeds: principle.

We’re not saying that principles are better than rules. Principles and rules often work together. If God has commanded that you shall not steal, lest you burn in the fiery pit of pain and suffering, that’s a rule worth following. In fact, it’s so worth following that you may consider adopting it as one of your principles. You would then make a rule into a principle.

Of course, you don’t always need to make rules into principles. Say your family has a rule that you always finish homework before watching television. It’s still optional for you to elevate that rule to a principle. You may be content to simply follow the rule so you don’t get in trouble rather than personally embracing it and making it one of your principles.

Kant, an 18th century philosopher, noticed the importance of principles in ethics as opposed to mere rules, and he turned that insight into one of the world’s great ethical systems. Kant thought that one single, supreme underlying principle — which he called the categorical imperative — gave rise to all other ethically important principles. He thought this underlying principle was accessible to everyone by the use of something called practical reason, and he thought that the binding force of that principle had little to do with either the consequences of one’s actions or divine commandments. Although large amounts of philosophers are still trying to hammer out the specific form that an ethics of principle should take, to this day philosophers call it Kantian Ethics.

At the root of Kantian ethics is the value of practical reason, or rationality, which Kant believed separates humanity from animals. This faculty gives humans a special kind of dignity that’s not present in the rest of the animal kingdom. Very simply, practical reason is the ability to set ends for yourself. Practical reason makes Kant’s theory different from ethical theories like utilitarianism, which aims at making other people — and animals — as happy as possible. Kant wasn’t just a grumpy old man. He wanted people to be happy; he just thought happiness shouldn’t be the last word on ethics. Instead, he thought ethics was about living a life guided by reason.

Kant believed that the principles you live by should be those forged by your very own practical reason. So the defining struggle in an ethical life is the battle between two forces that motivate human actions:

• Inclination: Acting from inclination is when you’re motivated by what you naturally want to do. Inclinations are your natural habits.
• Duty: Acting from duty is when you’re motivated by the principles forged by practical reason. Duties are principles given by practical reason.