Is there anything in this world that we can be 100% sure about?

A complex question. Being sure can be read as a psychological state, a feeling of complete confidence. And of course we are, as a matter of fact, completely confident about a lot of things. At least I am. But the real question is whether we are entitled to that feeling. That raises the question of what kind of entitlement is relevant. Is it pragmatic entitlement? That is, does such confidence yield good outcomes? It seems to. Or would it require proof beyond the possibility of refutation? The latter raises hard questions about what proof is and about what refutation is. What would a starting point for a proof be? How would you justify the form of argument you use? But how would you decide what to take seriously as a refutation? You can see that this is not a simple matter. I suggest that you read Sextus Empiricus, OUTLINES OF PYRRHONISM and then later, Wittgenstein's ON CERTAINTY to get a feel for how much fun and how hard it is to think these questions through.

What's the moral problem with pornography? As far as I can understand it, it hinges on the concept of 'objectification', which seems to mean treating someone else as a means to your own ends rather than as an end in themselves. But if I go to the corner shop to buy a pint of milk, aren't I treating the guy behind the counter as a means to my own ends (buying a pint of milk) rather than as an end in himself? Does buying milk have the same ethical status as pornography?

But also note that there is a lot of reasonable debate about this, and there are those who defend the moral permissibility of pornography as a form of commercial exchange in which all parties who participate voluntarily benefit. Note also that communities and subcultures vary quite a bit in attitudes towards pornography. One does have to consider the facts at some point: what is the psychological effect of consuming pornography on its consumers; what is the impact of pornography on those who model or act? What is the impact on social values and the treatment of others? There is surprisingly little consensus regarding these data.

I have a 12 year old dog. She's no longer in great health, doesn't qualify as cute or attractive, and has rightfully been accused of stinking up any room she remains in for more than a few minutes. Still, she's my dog and I love her. Unfortunately, I am in a situation that requires that I move to a place that won't allow me to bring her. I can't find anyone to take her and am pretty sure that if I take her to the animal shelter she will spend a terrible 2 weeks there, not be adopted and then be euthanized. I've been thinking of taking her to a veterinarian who will put her to sleep with a painless injection while I'm there with her. I know this will break my heart, but is it the right thing to do?

I agree that this is a hard one, harder of course for you than it is for us, and harder for us than it is for your dog. The last is an important point. Euthanising your dog in this situation will cause you a great deal of suffering, but will not cause the dog suffering. It will deprive her of future pleasure of course, but she will not suffer from knowing that. I think that condemning her to spending her last few weeks without you in a cage would be cruel, and recommend against that course of action. Of course, if you can, you might arrange a private adoption. But if you can't, I think that euthanasia is the most humane option. You can ease your own feelings of guilt by remembering that. But you probably can't do much about the reasonable grief.

Why does anything exist? Wouldn't it be more believable if nothing existed?

This is an interesting question. If you want to explore it through a text, I recommend Schopenhauer's On_The_Fourfold_Root_of-the_Principle_of_Sufficient_Reason or Wittgenstein's "Lecture on Ethics." Note that usually when we ask "Why?," we mean to ask how something is to be explained given some background conditions . But the question, "Why is there something rather than nothing?" precludes the background against which the "Why?" makes sense, and so might really not be a real question at all, so much as an expression of awe, or something. And if nothing existed, there would be nobody to believe it at all! Your existing is a precondition of being bothered by the question in the first place.

What, if anything, can you boil one's self down to, outside any notion of soul or essence?

Many philosophers, especially those in the Buddhist tradition (Nagasena, Candrakirti, Santideva,or see Hume for a Western sympathiser), have argued that there is nothing that one can "boil oneself down to," that is, that the self has no existence independent of convention. Others have argued that there is some basic subjective entity, either substantial (Descartes) or transcendental (Kant, Schopenhauer) that undergirds our identity.

We are often told time is like a river. Are there other useful analogies for time? For example: Time is like a bowl of jello with fruit: time is the jello and events are the fruit stuck in it. I guess what I'm really asking is does time have to flow? Is there another way of thinking about time?

Thinking of time as flowing obscures far more than it clarifies, on my view, and I think that the river analogy is dangerous. Anything that flows flows at some rate. How fast does time flow? Sixty minutes per hour? The image raises the prospect of a supertime against which the flow of time occurs, and that raises a nasty regress. Better to think of time as a dimension of the universe, but one that is anisotropic,t hat is, one in which going in one direction is different from going in another, unlike, say, East-West travel.