I think the two distinctions you make are the right ones to make. I doubt that the four necessary conditions in your definition of 'terrorism' are jointly sufficient, but I'm not too concerned about that. [And I didn't claim that they are jointly sufficient, only that they are individually necessary.] I was hoping for a good practical definition and this is as good as I've seen (and better than the ones I offered). If the State Department were to adopt this definition, they would have a good, functional definition that got nearly every case right. It's too bad that you and I both know the State Department as currently staffed and run would never do anything so sane!
Title 22, Chapter 38 of the United States Code (regarding the Department of State) contains a definition of terrorism in its requirement that annual country reports on terrorism be submitted by the Secretary of State to Congress every year. It reads:
That is fairly close to what I said, though I wasn't aware of this definition until just now. I didn't mention premeditation, but that pretty much goes without saying. There are plenty of spur-of-the-moment crimes of passion, but how many spur-of-the-moment terrorist acts of passion are there? But three of my points are covered.
Here's my attempt at a counterexample. Suppose we are in Nazi Germany and suppose further that the Nazi state was not a legitimate one. Thus, in Germany during Nazi rule, there was no legitimate state. I am part of a German underground agency working to overthrow Hitler's regime because I and my agency recognize the Nazis as illegitimate and murderous. My agency is clearly not a state, so I think it meets condition three. My agency and I have a political goal: the overthrowing of the Nazi regime and the establishment of a legitimate government. So, condition one is met.The other two conditions might be a little harder to meet. Suppose I know that Hitler is to give a speech at a rally, flanked by many high ranking Nazis. My agency has found a way to get myself and a few others into the crowd, but we know the Nazis thoroughly check a crowd for guns. Luckily, agent X is an ace explosive maker, and can make explosives out of things that not even the Nazis would suspect. Agent X equips us all with highly explosive cigarette lighters. We want to kill as many of the Nazi brass as we can and this may be the best shot we have. Given the circumstances, we do not have the option of discriminating between the "combatant" Nazis and the civilians who may have just come out of curiosity. We decide it is better to risk killing a civilians who are too close than not take the opportunity. Thus, we seem to meet condition two.The question is whether this counts as an act of sabotage against the Nazis. It certainly involves the killing or maiming of other human beings. And, you might think that sabotage involves acts against legitimate entities, and the Nazis are not legitimate. It seems to me to be more than mere sabotage. But I think someone could reasonably disagree with me about that. If I'm right, then it appears that I'm a terrorist unless we come up with more conditions.