I could come up with an argument that you don't exist, but it would be harder for you to. Descartes' point is that even in doubting that I exist, I seem to presuppose that I actually do. Descartes claimed that in any moment when I reflect on it, I know for sure that I exist. That said, this shows much less than it might seem to. In particular, it doesn't show that there is any unified "self" that has a continued, coherent existence over time. The existence of that sort of "I" has been doubted by many thinkers, going back at least to the Buddha, but also, famously, by David Hume and more recently by Derek Parfit. Views of this sort are sometimes called "bundle theories" because they replace the idea of a unified self with a picture according to which we are an ever-changing bundle of sensations and thoughts. Here's a link to the section of Hume's Treatise in which he sets forth his views on the self. Enjoy! http://www.mnstate.edu/gracyk/courses/web%20publishing/TreatiseI.iv.vi.htm ...

To know something, I need to believe it. If by over-thinking or thinking unproductively I talk myself into a state of doubt, then I won't know what I formerly knew simply because I no longer believe it. Of course, if the doubts are a sort of passing intellectual vertigo, wemight well say that I really knew whatever it is all along, eventhough I had temporarily put myself out of touch with the angels of my own epistemic better nature. At least, that's the short story. The long version would get complicated and would best be provided by someone who thinks more about theory of knowledge. (And indeed... I noticed after I submitted my reply that Nicholas Smith had already given a more complkete answer a few minutes before!) But yes: there are such things as over-thinking, analysis paralysis and the like. My sense, however, is that the more common problem runs in the other direction: leaping to dubious conclusions without much of anything in the way of reflection, as Prof. Smith suggests.

Perhaps we need to ask a prior question: why would we make such a challenge? And living in a country where large numbers of people are suspicious of evolution and think that people who worry about global warming or nutty or part of a conspiracy, I'm not so sure that society really is "science worshiping." If you want to know the truth about the natural world, science is your best bet. That's because "science" isn't a secret cabal, but most importantly it's a set of intellectual methods that let us explore the empirical world systematically, weed out unpromising hypotheses, and gauge the strength of likely explanations. Does acupuncture work for back pain? The answer may well be yes. But anecdotes aren't enough to make the case. We need the kind of systematic techniques that we call science. At the other end of the spectrum, how many dimensions does space-time have? We may never know for sure. But it's a safe bet that our best answer will come from science. And on it goes. If rationalism ...

The difficulty here is with the idea that "objective reality" is a matter of consensus. I've heard that said often enough, though virtually never by a philosopher or a scientist. I must confess that I've never really understood what makes the idea seem plausible or attractive. Whatever the details, it seems reasonable to think that the world is the way it is whatever I think of the matter. The universe existed for eons in sublime indifference to the fact that we weren't around to have opinions about it, and after we mess things up and end our species' sojourn in the world, things will once again go on without somehow having gotten vague, fuzzy or unreal due to our absence. Gaseous gab about "consensual reality" is perennially fashionable in some circles, but the fact that some people are inclined to talk this way doesn't mean that it has a lot going for it. Of course, whether what we think about the world gets things right is another question. The plausible common-sense answer is that we're...

The answer I'd want to offer isn't "philosophical" in the sense of being some sort of response to skeptical arguments. It's more straightforward and more from the point of view of science itself, as it were. And the answer, in general, is just that we've gotten a lot better at measuring things, doing experiments and analyzing data. We've also got a great deal more data than we used to have. A comparison of sorts: when the telescope came on the scene, we came relatively quickly to the conclusion that we could say a good deal more, a good deal more reliably, about the heavens than we could before. Similar comments apply to the old-fashined optical microscope, and even more so to devices like the electron microscope. Likewise, as statistics came into its own, we got a good deal better at analyzing data and drawing robust conclusions from it. It's arguable that the kinds of modeling techniques that computers have allowed us to develop are yet another example. So at least part of the answer has to do with...

It might help to start with some definitions. As philosophers and logicians use the term "valid," a piece of reasoning is valid, roughly, if it's impossible for the premises to be true unless the conclusion is also true. That means that any argument with true premises and a false conclusion is automatically invalid. And as philosophers and logicians use the word "sound," a sound piece of reasoning is valid and has true premises. That means that any sound argument automatically has a true conclusion. Of course, valid arguments can lead us to bad conclusions. That happens when they start with false premises. The following argument is valid, but the conclusion is false: Some whales are fish. All fish have gills. Therefore, some whales have gills. The problem, of course, is the first premise. But the reasoning isn't at fault. So far, we've talked about deductive reasoning, and we can say that there are principles of deductive reasoning that are reliable in this sense: when applied to true...

Others may have things to add, but one obvious way is that many of our beliefs about the past are caused by things that happened in the past and produced traces, either directly or indirectly, in our brains. But on the usual view about how the universe is wired up, our beliefs about the future aren't caused by future events. This doesn't make knowledge claims about the past uniformly more secure than knowledge claims about the future. Some facts about the past may be well nigh inaccessible; their traces may be faint or non-existent, and there may be no good general grounds for inferring. (For example: I'd guess that there's almost no hope that anyone will ever know exactly how many people were on the swath of ground now marked out by the University of Maryland campus at noon on April 3, 1808. But -- skeptical worries aside -- we can reasonably claim to know that the earth will rotate on its axis over the next 24 hours. Still, knowledge of the past has a certain priority. Our knowledge that the...

Let's start with the more general question: is it possible to recognize evidence of something that we had no experience of before? The answer seems pretty clearly to be yes, since we've frequently found good reasons to believe in various such things. We have evidence for black holes, for example. We have evidence of the existence of various exotic particles. Although the details are complicated, the way this works can be explained in this sort of way: We're interested in whether there are Xs. We ask: what would we expect to see if there were? What evidence E would Xs produce? And how likely is it that we'd find E if there were no Xs? Assuming that the "prior probability" of Xs isn't too low (assuming, for example, that Xs would have a sensible place in our larger scheme of things), assuming that the probability of E given X is appreciably greater than the probability of E given not-X, finding E might well give us good reason to think there are Xs. Or at least, this is a fairly common kind of story...

Or tiny pieces of tinfoil! One way to think about your question is from the day-to-day point of view of ordinary knowledge. From that point of view, we know -- or take ourselves to believe reasonably -- that your dog doesn't run the world because there isn't the slightest evidence that he does and a good deal of evidence that he doesn't. Unless I'm much mistaken, your dog shows the usual signs of doggly limitations. We seem much better at manipulating him than vice-versa. Most of what we do doesn't have any obvious connection with anything that Poochie shows the slightest signs of caring about. In fact, there's no reason to think that Poochie has much of anything in the way of thoughts about who controls what or about what we think. (Poochie probably doesn't have a "theory of mind," as some people say.) Another way of taking your question is as a humorous way of asking how we know anything at all. In some weak sense of "possible," it's possible that the whole world is under the control of...

I just posed this question on your behalf to a colleague of mine. Here's what he said he'd tell you: "No!!! But you're wrong..." I suppose we could add: it depends on what you mean by "prove," "objective" and "data." In this case, it also seems to depend on what the meaning of "is" is. (Your hand is a parrot? ) but I think at the end of the day, my colleague's answer would still be more or less right. (Not that I think you really believe your hand is a parrot...) The more serious point: there's no airtight refutation of skepticism, or so many philosophers would agree. But many philosophers would also agree that this doesn't give us a reason to worry about skepticism. As my one-time colleague Dudley Shapere once put it, the possibility of doubt isn't a reason for doubt.