It has hitherto been assumed that our cognition must conform to the objects; but all attempts to ascertain anything about these objects a priori, by means of conceptions, and thus to extend the range of our knowledge, have been rendered abortive by this assumption. Let us then make the experiment whether we may not be more successful in metaphysics, if we assume that the objects must conform to our cognition. This appears, at all events, to accord better with the possibility of our gaining the end we have in view, that is to say, of arriving at the cognition of objects a priori, of determining something with respect to these objects, before they are given to us. We here propose to do just what Copernicus did in attempting to explain the celestial movements. When he found that he could make no progress by assuming that all the heavenly bodies revolved round the spectator, he reversed the process, and tried the experiment of assuming that the spectator revolved, while the stars remained at rest. [From The Critique of Pure Reason]

Some have criticized my writing style as ponderous and incomprehensible. Okay, I'll admit, even I have criticized my writing as ponderous and incomprehensible. But still, why have people had so much trouble with this passage? All I'm saying is that I'm doing what Copernicus did; he said that the sun rather than the earth was the center of the solar system, and I'm suggesting we have to do the same thing in philosophy.

My point is that philosophers have always assumed that our minds must simply reflect the way the world ultimately is, and so they've decided that we have to inquire deeply into reality. But I ask: if that were the case, how could we know anything about the world a priori—that is, in advance of any experience? How could I know, for example, that every event necessarily has a cause? How could I know that every American Idol first stage winner will say: "I'm going to Hollywood"?

My proposal, then, is that we have to radically shift our perspective, just like Copernicus did. Rather than assume that our minds simply mirror the world, we must assume that the world—certain features of the world, anyway, or the world as we see it—reflects the structure of our minds.

It's as if I had a pair of blue sunglasses that I could never take off: I would know for certain that whatever I saw was blue, but that would be a characteristic of my perspective on things; it would have little or nothing to do with how those things look in themselves. So really what I'm saying here is that our attention in philosophy should properly be focused on our sunglasses rather than what we see through those sunglasses.

That something happens, then, is a perception which belongs to a possible experience, which becomes real only because I look upon the phenomenon as determined in regard to its place in time, consequently as an object, which can always be found by means of a rule in the connected series of my perceptions. But this rule of the determination of a thing according to succession in time is as follows: 'In what precedes may be found the condition, under which an event always (that is, necessarily) follows.' From all this it is obvious that the principle of cause and effect is the principle of possible experience, that is, of objective cognition of phenomena, in regard to their relations in the succession of time. [From The Critique of Pure Reason]

Okay, so you remember how I told you there are two faculties of the mind—the intuition and the understanding? And remember how I suggested that there is an a priori (or "pure") aspect to each? If you answered "yes" to these questions, you are immediately awarded a Kantian Gold Star. You'll also be in a good position to appreciate that in this quote, I'm talking about the "pure" part of the understanding—in particular the category of causality. 

I have Hume in the back of my mind (wasn't that a country song?) as I write this. Hume had claimed that you could search experience all you wanted, but you'd still never find the notion of cause—so therefore causality is just an illusion. It's intriguing, like most of what that guy says, but you just know there is something wrong with that claim (that's also a feature of most of what Hume says).

So, what I'm saying in this passage is that while it's true that you can't find causality in your experience, that does not therefore mean causality is a mere illusion. On the contrary, it is what I like to call a condition of the possibility of experience. That is, we must always assume that a given perception is causally linked to another particular series of perceptions—i.e., that there is a rule determining a thing "according to succession in time." If we didn't make that assumption, we would never be able to have the experience of an event in the first place.

Causality, I'm saying, is a concept that enables us to view the world as something involving orderly sequences of occurrences. Without that concept, our experience would be a total jumble—sort of like a permanent version of Lost.

The moral worth of the action thus lies not in the effect to be expected from it; thus also not in any principle of action which needs to get its motive from this expected effect…Nothing other than the representation of the law in itself, which obviously occurs only in the rational being insofar as it, and not the hoped-for effect, is the determining ground of the will, therefore constitutes that so pre-eminent good which we call 'moral', which is already present in the person himself who acts in accordance with it, but must not first of all be expected from the effect. [From The Groundwork for the Metaphysics of Morals]

Here I am answering your question about the ultimate basis of morality. What do you mean you never asked that question? Of course you did—you just didn't realize it.

Maybe you think the moral worth of an action lies in that act's consequences: for example, telling the truth is a good thing because by and large it makes people happy. Well, nope—you're wrong. Telling the truth is good, of course, but the consequences of doing good is not the reason why it is good in the first place.

So, perhaps you think I'm just saying that moral worth lies not in the consequences of an action but in the motive for doing it? You're getting warmer, but that's still not quite right. It's not just the motive—or what I would call the will— that matters, but the nature of the principle that is causing or determining the will.

I'll give you one of my own examples from the Groundwork for the Metaphysics of Morals. Let's say it is wrong to commit suicide. Now, suppose we have an ordinary, reasonably happy person who intentionally refrains from killing himself. Does his action have moral worth? No, because he likes his life. In my language, his will is determined by an "inclination" (feeling) rather than by a rational principle. His action, in this case, is not wrong; it is simply morally neutral.

But now imagine that the same person suffers various hardships and becomes despondent. Suppose, even, that he falls into a deep depression. He actually wants to commit suicide but refrains from doing so only because he knows that it is wrong to do so. Only now does his action have genuine moral worth, as it is the moral law itself that is the "determining ground of the will."

You may not agree with me on this—believe me, I've gotten a lot of grief for my position. I know it sounds as if I'm saying that you can only be moral when you hate doing something. That's not quite what I mean, but if this interpretation encourages a few do-gooders to wipe those smug grins off their faces, I'm all for it.

In fact, though, my real point is that we must look to the principle determining the will if we want to understand morality. Only when it is a moral principle alone that is causing the will to decide in the way that it does can we call an action genuinely moral.

There is therefore only a single categorical imperative and it is this: act only in accordance with that maxim through which you can at the same will that it become a universal law. [From The Groundwork for the Metaphysics of Morals]

A categorical imperative is a moral command, a claim like You must not lie, or Every candidate on The Bachelor, male and female, must always insist that they are looking for their best friend (perhaps not a moral command in a strict sense, but necessarily true nonetheless). I am claiming here that there is, at bottom, only one moral command, from which all the particular commands with which we are familiar can be derived.

But what's this business about "maxims" and "universal laws"? A maxim is a principle that guides my action: if, for example, I make a habit out of secretly removing money from the lunch boxes of fourth graders, my maxim is: Stealing from children is a good thing. My suggestion is that if a maxim can, without contradiction, hold as a principle that everyone must follow, then we know it is a moral principle.

What I'm giving you here, then, is a little logical test to determine whether or not a given principle is moral. (Try it, it's free—though once you sign up you will be getting repeated emails trying to sell you all sorts of Kant Products.) Let's say you are considering borrowing money from your friend, promising to repay the loan when you know it will not be possible to do so. The maxim of your proposed action is: You can make a false promise to yourself out of difficulties.

Now, if you are a Kantian, you will attempt to universalize this maxim. You ask yourself: what if everyone acted in this way? Not only would it be a sad world, but it would also be a world in which promises had lost all their meaning. Nobody would believe anyone else's promises anymore.

But it's worse than that. For in order for you to act on this maxim, you will have to assume the existence of the very practice of promise-making that your own maxim would destroy! Translation: you can't break a promise if there aren't any promises in the first place, so your maxim destroys itself in a contradiction.

Keeping your promises is a moral principle. In the same way, I show that all our moral duties follow logically from a single principle—that a maxim is moral only as long as it can be made universal.