We all know the old epistemological condundrum about trees falling in forests.

I have a similar one about the DPRK's nuclear weapons. Some in Washington have reason to believe that they already have them, and are firing up their nuclear plants to build more.

But nukes are kind of like missiles. They're finicky devices, and there are several things that have to be gotten just right. Ultimately (unless you have a lot of experience, and access to extremely classified simulation codes), you're not going to know whether or not they work unless you try them.

Recall that we did so at Trinity, and one of the reasons that we didn't do an offshore demonstration for the Japanese was that we couldn't be a hundred percent confident in the bomb working, and we only had a couple in the inventory, and it would have taken a while to build up the fuel supply to build more. If we'd told the Japanese that we were going to show them how it worked, and it didn't, it would have damaged our credibility. With the actual bombing, if it hadn't worked, no one would have been the wiser--the airplane would have just turned around and flown home, and anyone who saw it would have just assumed that it had gotten lost.

The North Koreans are in the same boat, if they've built a weapon or two. They can't know for sure that it will work. They've done missile tests, but if they'd tested a nuke, even underground, we would have noticed. They simply lack the sophistication to do an undetected test (difficult even for us).

So while they may have a couple of devices that, in (someone's) theory, will create a nuclear explosion, I'm not sure that it's quite right to say that they have nuclear weapons. As the saying goes, in theory, theory and practice are the same, but in practice, they're different.

By the way, I suspect that the Israelis probably do have confidence in their weapons, even if they haven't actually tested one, because they probably are capable of reliably simulating them. And it remains possible that the flash that the Vela satellite picked up back in 1979 was an Israeli test.

I'm not sure what the policy implications of this are with respect to North Korea, but it adds at least one more column to the game-theory payoff matrix.

I think that we should have dropped the bomb on the summit of Mt. Fuji as a demonstration.

We only tested the Plutonium bomb. Its mechanism (implosion) was and is fabulously complex and demanding.

We did not test the Uranium bomb. Its gun-like mechanism was much simpler, and Uranium is much easier to make a bomb from. It was confidently dropped on Japan with no previous test.

So I would guess that NK can feel fairly confident that their weapons will work.