In describing Kant's idea of the "thing-in-itself" Thomas Pogge (in response to a recent question on this site) recently wrote that "According to this explanation, space and time are then features only of objects as they appear to us." I'm having a difficult time deciphering this statement. To me when you speak of a feature of an object you are referring to that object in-itself almost by definition. It seems like space and time could be either a feature of the world or a feature of our mind/cognition or psychic tendencies which we project onto the world but not both. To say that space/time is a feature of the world as it appears seems to involve a confusion of how language is used to speak about being. Appearances can reveal or distort being but I don't see how they can contribute to being. We don't speak of colors as features of the (outer) world as they appear to us do we? We try to figure whether colors originate in the mind or in the world and though we allow that there is some degree of interaction...

You are quite rightly puzzled by the distinction that Pogge, following Kant, draws between appearances and things-in-themselves: it's caused trouble for Kant's readers since the publication of the first edition of the Critique of Pure Reason . The distinction is, however, at the heart of Kant's project in the first Critique , and indeed, I would go so far as to claim that it's crucial to underpinning the entire Critical philosophy. (I see the first Critique as setting the foundations for Kant's overarching project, which I take to be aimed at ethics rather than at metaphysics and epistemology. This is a somewhat idiosyncratic view, but it is, I think, defensible; in any event, nothing in what follows turns on it.) Now the distinction that Kant wants and needs to draw is between the world as it is independently of human cognizers, and the world that appears to human beings. Yet Kant does not want to claim that the way things appear to human beings is merely a way that they appear, as...

Why is there a universe, rather than nothing at all? Is this a question that shall never be answered by science?

Why is there something rather than nothing seems to me to be a quintessential example of a metaphysical question, one that cannot be answered by scientific investigation. It is logically possible that science might come to explain how the universe came into existence--although the information necessary in order to answer this question may well be inaccessible to us, so that the question is practically unanswerable, but even if we had that information, the question of WHY the universe came into existence seems to call for an answer beyond causes investigated by science and thus to lead directly to metaphysics (and religion).

Is a universe where absolutely nothing exists conceivable without contradiction?

It does not seem inconceivable to me: especially if one draws a distinction between a universe and the objects in it, it certainly seems conceptually possible. And a brief search on the web suggests that this conclusion is not merely the result of uninformed, armchair speculation: click on this link.

If humans (or perhaps sentient beings) could be defined, what exactly are we? I have never studied philosphy, but when I studied media I was taught that we were 'automatons'(which seemed a little glib...though that shouldn't matter) and I've come across a few theories such as wavelengths etc. Is there an answer? I hope this isn't too scientific.

I think that it depends on what one is looking for in a definition. Aristotle famously characterized human beings as rational animals. (Of course, if other rational animals were discovered, it would follow from Aristotle's definition that they, too are human beings. So perhaps Aristotle's definition could be modified to constitute simply a definition of 'person' or 'agent': in which case the discovery of other rational beings than human beings would simply lead to the class of persons or agents being enlarged. For what it's worth, such a characterization would accord with Locke's discussion of personal identity in the Essay Concerning Human Understanding , where he distinguishes between the identity conditions of human beings and those of persons: the latter are such that beings other than human beings could fall within the scope of the concept, whereas the former is limited to human beings, that is, beings that look like human beings and manifest the form of life shared by other human beings.)...

Do categories exist? For instance: Animal. "Animal" is the name of a category, a set of things within certain parameters. Now, the animals themselves exist, but does "Animal" exist? After all, isn't "animal" just an name, an idea we have "created." That which composes a category exists, but does the category itself exist?

This is a version of the question of whether universals exist, about which there has been considerable philosophical discussion over the past 2500 years or so. Some philosophers--call them 'nominalists'--believe that the only things that exist are particulars: in the case of animals, then, only particular sloths, rabbits, dogs, etc. exist; some philosophers--call them 'realists'--believe that not only particulars, but kinds , or universals--in the case of animals, the kind 'sloth' or 'dog' or even 'animal' itself, distinct from particular instantiations of that kind--exist. (Some realists even believe that kinds or universals are the only real things, and that particulars aren't real, or at least not real in the same respect that universals are real.) It seems to me that where one stands with respect to the universalist/nominalist divide may in part reflect one's account of cognition, or how one comes to know things: if one believes that the senses are the only source of knowledge, then one may...