The details are complicated. But what I'm interested in here isn't so much the morality part as the choosing to act part. In Kantian philosophy, the idea is that because we are free and can reflect, we can only act when we have rationally endorsed the law, or principle, of our action. So, for instance, suppose you have a desire to eat bacon. That desire does not give you a reason to act, all alone. Instead, because you are able to think about your decision, you have to ask yourself whether to endorse this desire -- do you have a policy of eating bacon whenever you feel like it? Or a policy of only sometimes eating bacon when you feel like it? Or never? You have to reason about whether to act on the desire. So ultimately rationality sanctions your choice and you cannot act directly on a desire, even if you wanted to.
A cat doesn't face these choices because it can't reflect: the desire goes straight to the action -- unless, of course, there are competing factors like a person who sprays water in the cat's face to keep it away from breakfast. But those are just further desires -- in that case not to get wet -- and not reasons.
So, humans, unlike cats, have to act for a reason. Kant used this set up to show that, as in the example of not lying, you could have reasons for acting that were based on no desires at all. And thus we have morality and cats don't.
Hume said that "reason is, and ought only to be, the slave of the passions." That is, reason can never be a source of information about what one ought to do -- except in the trivial sense that if you want something you might use reason to get it. Like, if you want bacon, you might use reason to figure out how to get to the store to get some and cook it up nicely.
In Hume's version of human behavior, if you don't act on your desire it's not because you didn't endorse it as in the Kantian version -- it's instead because, just like the cat, you had some competing desire. So if you love pigs, you might decide never to eat bacon. But the reason doesn't come out of nowhere, it has to be based on a desire.
This sounds complicated -- and it kind of is -- but the part I'm interested in is this. For Kantianism, the difference between you and your cat is -- or ought to be -- profound, because while your cat is all about desire, you are all about reason and rationality. For Hume, the difference between you and your cat is ... details details. You're basically the same: wanting stuff and trying to get it. The difference is just you can talk and think effectively about the future. If your cat had access to these abilities you guys would be the same.
Now there are a lot of philosophical questions about which I have no strong intuitive feeling. But this isn't one of them.
Because I am with Hume. I am so with Hume on this question I have trouble making the other side sound good. You tell me I'm a bundle of competing desires who uses reason to try to figure out what best to want, you tell me that when I act like a nice moral person instead of a moral monster, it's because I basically care about other people, you tell me that while it might be perverse to want what is bad for me overall, it is not irrational, and I'm like, Yes, That Is Me. That is how I experience the world.
It's normal in philosophy to think of these two views as competing theories about what we all are like.
But I have this peculiar and frightening daydream in which it's not two theories about the same group of people, but instead that there are two kinds of people in the world: people who actually act on reason alone -- the Kantians -- and people who are just animals who also happen to have speech centers, day planners and the internet -- the Humeans.
I figure the way it happened is like this. Evolution gave us early humanoids, who became Humeans, and who gradually evolved the cognitive abilities that allow us to plant crops, play backgammon, and write Lolita.
Then at some point, long long ago, aliens came. These aliens were super-Kantians -- which means they not only could act on reason alone, but always did so. Temptation, lust, gluttony, the love of addictive drugs -- these things were totally unknown to them. Valuing rational nature, which they had, they did what they had to do to perpetuate it.
At this point the details are a little foggy. Did the Kantians have to mate with the Humeans to ensure the propagation of their species? Did the Humeans trick them into having sex with them? Not clear. But whatever happened, the Kantians passed on their rationality to some descendants, who are some of us. And now here we all are, driving each other crazy.
At the very least, there's an element of fear. If you're a Kantian, I imagine the image of humans as driven by desire is very scary. I mean, it's one thing if the desires are for peaceful harmonious living and so on. But there are also desires for mayhem and violence. What's to stop us from killing each other? Just the contingent fact that we generally like peaceful co-existence? That sounds so flimsy!
But if you're a Humean, the image of humans as driven by reason is also scary. Because if the question is what's to stop us from killing each other, and the answer is "it would be irrational," that hardly seems any better. It almost seems worse. Because it invites the reply, So What? The mental image of a world of people who refrain from hurting me not because they desire peaceful coexistence and care about others, but because reason requires them to do so -- well, that is a cold, cold world.
I hope we can manage our mutual suspicion without any big show-down. Because you can see how the fight would be deathly in its being so evenly-matched: knowing one's behavior is based in reason gives a person tremendous confidence that he is doing the Right Thing, a confidence that overrides all kinds of human impulses. But, of course, we all know that feeling and desire, when they're strong enough, override everything.
In my Humean way I'm all for peaceful coexistence. If you're a Humean too, you're already with me. If you're a Kantian, try to remember: we Humeans may be more variable and less predictable than you, but we have our good qualities, and most importantly, we care about you.