Are conjoined twins one person or two? That's easy. They have two minds, so they are two people. A person is defined by his or her brain. Your limbs, hair, lungs, heart, and all the rest of your parts can be transplanted, conjoined, or in some cases deleted, yet you remain the same person. You are your brain.

Now consider regular identical twins. Their brains have the same DNA, yet they are considered two people because their brains operate independently. I think we'd all agree that having the same DNA doesn't make twins one person.

Now what about the individual whose two halves of the brain are separated either by an accident or by surgery? Do you end up with one person or two? The two halves can operate independently, as shown by so-called Alien Hand Syndrome, where half of your brain is telling your hand to do one thing while your other half is wishing it didn't. In my opinion, that's two people occupying one skull. If you went into a voting booth, I expect that the alien hand could vote for one candidate while the other side could make a different choice.

Now I make the leap from something mildly interesting to something totally ridiculous. You should leave now if that sort of thing bothers you.

It seems to me, based on observation, that what we think of as one person is always two, even if the two halves of the brain are communicating. You wouldn't label twins as one person just because they communicate before they make decisions. It's the independent thought that defines a person, not the degree of their communication. If twins made a deal with each other to always make the same decisions, effectively acting as one, we would still know them as two individuals because they can think independently.

Sometimes when I'm alone in the house at night, I am certain the place is haunted while simultaneously certain that ghosts do not exist. Perhaps the right side of my brain is generating the thoughts of imaginary ghosts while the left is being rational. I realize that the human brain is a bit more fluid and complicated than the left-brain-right-brain model suggests, but I'm guessing that any time we hold two contradictory views at the same time, the two hemispheres of the brain are thinking independently.

Sometimes you might have three or more choices and you can't decide which one you prefer. But I'll bet your brain needs to consider them one at a time, in a serial fashion, if they are all rational choices. That's different from the ghost example, in which the sensation is that you believe the ghosts exist while simultaneously knowing they do not. It takes two brains to simultaneously have two contradictory beliefs.

I also think the two brain theory explains why people who are smart in general can hold irrational world views. In my experience, people who hold irrational views are almost always aware of their own irrationality. They simply have two brains, and the rational one doesn't always get to make the final decision.

Now suppose you could do a brain scan and determine which side of a person's brain is most active while pondering a particular political question. If the scan shows that the rational hemisphere is clearly in charge, you allow that individual to vote on the issue. If the irrational side is overly active, you politely explain to that person that he or she has to sit out this vote.

No, it's not a practical idea. But the cool thing is that I know it's a bad idea while simultaneously imagining it could work.