Michael Sandel is a modern Harvard professor, philosopher, and writer who has attempted to popularize philosophical thinking about justice in his book Justice: What's the Right Thing to Do? Kant's categorical imperative is absolutely essential to any philosophical discussion of justice, so Sandel treats it in great detail in his book, devoting an entire chapter to this concept. As he writes, Kant described a categorical imperative as one that did not depend on anything else, including causes or consequences:
For Kant, a categorical imperative commands, well, categorically—without reference to or dependence on any further purpose. "It is concerned not with the matter of the action and its presumed results, but with its form, and with the principle which it follows...[W]hat is essentially good in the action consists in the mental disposition, let the consequences be what they may."
The extended quote Sandel uses from Kant illustrates the crux of his concept of a categorical imperative. The principle of an action determines its morality, not its consequences. So the question from a perspective of justice is to determine what principles are right. Sandel goes on to describe how Kant addresses this question. He explains that people should act only according to principles that they would like to see become universal law. Kant also wrote that moral acts must treat humanity as an end, not a means. In other words, moral action must respect the rationality of humanity. In all cases, Kant did not take the consequences of actions into account. This, as Sandel shows, is the difference between a categorical imperative and hypothetical one. Hypothetical imperatives are contingent on the consequences of the action. Rational humans are free to act according to morality, and for Kant, this means acting according to a categorical, not a hypothetical, imperative or motive. This was true even when acting this way carried a possible (i.e., hypothetical) disadvantage or negative consequence. Because people could only control the motives of their actions, not the potential consequences, free people would make rational decisions according to categorical imperatives.