| Immanuel Kant created an ethical theory in 1785 with the work Groundwork of the Metaphysic of Morals. This ethical doctrine was derived entirely from reason. Kant is referred to as an armchair philosopher for this work, being that he simply thought about ethics and came out with this philosophy. So, what exactly is Kantianism and how does it work.
Kantianism focuses on intentions. If the intent was good, then the overall act was good. Suppose you wish to walk an old woman across the street and she gets hit by a bus. You intended to do a nice thing, and by Kantian standards, it was a good thing, even though she got hit by a bus.
How does this work. The intent is comprised of two things. One is the rational good will, the other is the irrational desires, or inclination. A perfectly moral Kantian would have few inclinations, or self-interests. This person would be constantly looking out for everyone else. An immoral person would follow inclinations and only inclinations. Thus, this person would act in their own self-interest all the time.
This brings us to the categorical imperative. It is kind of similar to the Golden Rule only it goes farther. The categorical imperative states that one should act as if their actions would become universal. Thus, everyone acts as I act. A moral person is one who does not act in their self-interest, but solely in the interest of others. We would like a moral person to follow the categorical imperative, that way everyone is helping everyone else out, and thus promoting life.
Morality lies in following the categorical imperative. To see if an intention is moral, run a test to whether or not there is a contradiction. Take suicide. The intention is to end life. The categorical imperative aims at promoting life. A contradiction is reached, and as such, suicide is immoral by Kantian standards.
Since no one acts completely in the interest of others, living under Kantianism is very demanding. Many actions are not moral, but instead are amoral. Suppose I take a teaching job to make money and to help out students. I am acting on my desire to make money, but also the rational want to help out students learn. Since I am acting with both reason and inclination, my action is amoral. | 
