It is unlikely that extraterrestrials have ever visited earth

This article, especially the parts about justified belief, is particularly relevant to this debate. In fact, it is the discussion of propositional defeaters (the good kind) that are the most helpful for my main objection to the resolution. Let’s imagine that Philochristos had argued that aliens had never visited Earth. This, incidentally, is my own belief. This belief is justified on the grounds that there is no evidence of such a visit. However, let’s imagine that we had knowledge of billions of nomadic extraterrestrials who had visited most of the planets in our galaxy. In the context of this new knowledge, our belief would no longer be justified, although we might still be right by chance. Quoting from my opponent’s own source: “The generic idea is that a person S knows p only if there is no true proposition, d, such that if S were to believe d (or d were added to S’s evidence for p), S would no longer be justified in believing p. In other words, the existence of certain unpossessed evidence prevents a person from actually knowing p if this unpossessed evidence would result in a loss of justification were the person to acquire the evidence, be aware of it, or recognize it. So according to defeasibility theories, it’s a true proposition that does the defeating, not a believed proposition. ” Of course, my opponent did not argue that extraterrestrials have never visited Earth. He argued that such a visit “is unlikely”. A much bolder claim. In round 2, he presented a syllogism, each step guessing at the probability of extraterrestrial behavior. I’m not at all certain that a syllogism so stuffed with vague probabilities and likelihoods would be valid, but I will concede the point to my opponent because it doesn’t matter here. Surpassing all this is the question: can my opponent assess the likelihood of any aspect of extraterrestrial behavior? No, he cannot. He is entitled to any kind of belief about extraterrestrials, of course. However, in the absence of knowledge of extraterrestrial behavior, it is impossible to make any scientific assessment of the likelihood of their having visited Earth. My opponent cannot do it, and therefore he cannot meet the burden of proof in this debate. *** When my opponent talks about “undercutting defeaters”, I think he is referring to my observation that his extraterrestrial fictions are inspired by his experience of terrestrial life. Of course they are. But this is irrelevant to the central argument. Even if his fantasy of extraterrestrials was quite unlike those on Earth, the main argument would still hold: that any claim about likelihood is belief, not fact. Unlike my opponent, I have never sat around with friends speculating about extraterrestrials. I’m not really into science fiction. Such a non-preference might be almost offensive on a site like this, I know, and I apologize. The reason I mention it is because when I countered my opponent’s extraterrestrial fictions with my own suggestions, the effect was regrettably raw. His space fantasies are far, far more compelling than mine. However, fiction doesn’t transform into fact just because it’s really good. *** This is one of those situations when it's difficult to be rational. I know that if I were at a party, holding a glass of wine, listening to my opponent's theory, I would be smiling and quite genuinely agreeing with him. This would be partly due to my opponent's charm and persuasive abilities, I'm sure, but also because this is a thinking bias that comes naturally to humans. I have never seen extraterrestrials, I don't believe in extraterrestrials or spaceships or any of the rest of it, and it seems a tiny, tiny jump to claim that a visit from extraterrestrials is "unlikely". But it's not a tiny jump. It's going from belief to false fact. This debate is as fun as a party, but it's not a party. We have to stick to reason and evidence, no matter how tedious it might be. *** Thank you, Philochristos, for creating this debate and for your impeccable conduct throughout, and thank you to anyone who has read this far. I will not be so brutish as to try and drum up votes or in any way stress the competitive side of this otherwise pleasant occasion. We all agree, I’m sure, that the only victory worth bothering about is the one belonging to Reason herself. *** 1. . http://www.iep.utm.edu...