It depends. Descartes would say no. The strength of his famous argument "Cogito ergo sum" (I think, therefore I am) is its "performativity", that is, its power to realize what is stated by the simple fact of stating it. But this performative aspect is lost if we declinate the same sentence in a past form. "I think therefore I have existed sometime before now" is a completely different inference. If I say "I apologize" I'm apologizing, while if I say "I have apologized yesterday" I'm just describing a fact about my past life, whose truth-conditions depend on many variables.

Whereas G.E. Moore would say that this is commonsensical. In his essay "A Defense of Commonsense" , he writes: " There exists at present a living human body, which is my body. This body was born at a certain time in the past, and has existed continuously ever since, though not without undergoing changes; it was, for instance, much smaller when it was born, and for some time afterwards, than it is now"

These are for him truisms, that is, commonsensical propositions that I can infer just from the fact that I'm here and able to think.

I'm not convinced by G.E. Moore commonsensical propositions, and I share your doubts about the fact that you can infer your past existence from you present state of mind. Descartes' performative argument is much stronger: if I'm thinking I can necessarily infer that I exist, but my past existence depends on a check of reality that goes beyon pure logical inference.

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 earth will rotate on its axis over the next 24 hours is based on things we know about the past and generalizations that this knowledge supports. Something like this is true in general: knowledge of future events is grounded in knowledge of the past, but not vice-versa.

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 about how we come to reasonable belief in such things. (It's a story, by the way, that's modeled on Bayes' theorem in probability.)

A little more directly: it's reasonable to believe in hitherto unexperienced Xs if we have some evidence that would be surprising if there were no Xs, but not surprising if there were.

With this in mind, we can read the second question as asking whether this sort of reasoning could lead us from sense data to reasonable belief in the external world. But before we try to answer that, we might want to pause and ask what it has to do with our actual situation. Are things really as the question presupposes? Are we really in the position of having only "sense data" as evidence, and trying to find a way to infer the existence of a hypothetical external world? It's not obvious that we are. A story that seems at least as plausible is that we experience the world. "Sense data" as the supposed internal objects that we're directly acquainted with are themselves hypothetical entities: parts of an eminently contentious tale. It seems at least as reasonable to say that when I look around, I see people, tables, chairs, chunks of cheese and such. I don't infer the existence of an outer world by some process of reasoning from "sense data." And though using my senses can provide data for various inferences (as when I see the light under the door and infer that John is in his office), we needn't reify by turning "sense data" into inner intermediaries.

This alternative story isn't without its puzzles. When I look into the sky, I may "see" a galaxy that no longer exists, as Bertrand Russell pointed out. But whatever we say about this problem, the best approach isn't likely to be by building a theory of knowledge on sense data.

Of course all this may be a way of making part of your point. If we were to view knowledge of the external world as inference from sense data, it would be tough sledding. Part of the reason is that the Bayesian story I told above couldn't get going. We wouldn't have any basis for saying that our "sense data" would be less likely if there were no external world.

The short answer is "no".

It might take "experience" and "culture" (in a broad sense) to understand some sentence or other representation M. But it certainly doesn't follow from this that we can't know (as "objectively" as you like) whether M is correct.

For a stark illustration of the point, take the case where M is a bit of mathematics, e.g. the claim "There is an infinite number of prime numbers". To understand it you have to call on some background experience in elementary mathematics (the practice of counting and so on). We might say that to understand this sentence requires being inducted into a bit of mathematical "culture". But the fact that your understanding of this claim might be said to rely on your mathematical "culture" in some broad sense, doesn't mean that (once you've got the understanding) you can't acquire objective knowledge whether the claim is true. In fact, the claim is a theorem, and you can get knowledge of its truth -- objective mathematical knowledge, by any sane standards -- by following one of the proofs.

Here's another illustration of the same point. Take the case where M is a road map. There are a lot of conventions involved in plotting the roads and landmarks (in maps produced in remote countries, the conventions can be rather different). To understand the map you need to understand which lines indicate which sorts of roads, which indicate railways or rivers; you need to understand that the width of the lines indicating roads is not on the same scale as the rest of the map; you need to understand which landmark symbols mean what; and there's more besides in learning to use such a map. We might say: to properly understand the map you have to get inducted, in some small way, into the cultural practice of map-making/map-reading.

But the fact that understanding maps requires acquiring a bit of "culture" (in the broad sense) plainly doesn't mean that what a map tells you can't be objectively right or wrong. Cambridge is north of London; and a map that says otherwise has simply got it wrong. But in fact, though maps can make mistakes, those produced by responsible agencies are hugely reliable. So they will give you geographical knowledge (again "objective" in any reasonable sense). For example, from Google maps you can get to know that Oxford is less than a hundred miles west of Cambridge.

I haven't checked my dictionary but I take it that a 'bias' is a favouring of one party over another that is not based on the facts of the matter - it is akin to a prejudice against one party. So I think that if you could discover that X had behaved wrongly more times than Y the judgement that 'X is more wrong than Y' would not show a bias towards either side but would simply reflect the objective facts of the matter. Thus it is possible to have an opinion on something and not have a bias, just in case your opinion matches the facts of the matter. On the other hand with cases of conflict, like the one you raise, it can be difficult to be sure that you really do have all the facts to hand and also that you have an appropriate way of 'weighing' wrongs against each other (is a suicide bomb which kills a child worse than a missile which kills ten civilians or vice versa?). So it may be that in these kinds of cases the charge of having a bias can always be made.

I agree that acknowledging that "the mere possibility of doubt doesn't provide a reason for doubting" is one part of a sensible answer to your question: that (1) we aren't sure whether we can prove complete certainty that your dog--or that Allen's scrap of tin-foil--does not control the world, despite all appearances to the contrary, doesn't provide us with (2) a good reason for taking seriously what certainly looks to be an extremely remote possibility. Moreover, and as the reference to tin-foil suggests, (3) there seems something irrational about taking those doubts too seriously.

But why do possibilities like these seem easy to ignore or even to dismiss as "crazy thoughts"? Is this just because we are unwilling to challenge received opinion? Is this dismissive stance yet another example of the human tendency to embrace dogmatism? I believe is what a student of mine had in mind as she stormed out of the classroom when I offered this sort of response to similar doubts that she had raised.

I think the reason why it is not a matter of petty dogmatism to conclude that we have no reason to take these possibilities seriously is that we have ample reason to believe that they do not describe our world. In this case (as in the case of my angry student, who was entranced by the idea that bears might have sophisticated religious practices that have hitherto escaped our notice), we possess a large body of relevant scientific findings that provide us with those reasons. Surely it is not simple dogmatism to note that there are significant findings of science that give us reason not to worry that the universe is controlled by your dog or Allen's scrap of tin foil!

One can certainly debate the strength of these reasons, and of course it is possible that it will turn out that they are not as strong as they appear to be – for example, this could occur if someone brings forth are strong arguments that the results of science are unreliable or are otherwise not worth taking seriously or if we gain unexpected new scientific knowledge about your dog’s powers. Likewise, if a philosopher brought forward powerful reasons to doubt that we actually know anything, those considerations might mean that it would be wrong to appeal to the present state of scientific inquiry to dismiss the possibilities you raise.

In the absence of such arguments or new scientific results, however, there does seem to be no reason to suspect that the world is run by that scrap of tin-foil lying under the stove and thus no need to worry about refuting this bare possibility. Or, put differently, the key is to combine philosophical anti-dogmatism with the insistence that philosophical reflection proceeds by careful argumentation.

If this is correct, this can teach us something about the nature of "philosophical reflection:"reveling in the exuberance of "bare possibilities" can be a useful philosophical attitude, but this attitude by itself is inadequate to lead us to interesting philosophical conclusions.

Finally, just as we ought to remain open to the possibility that there could be strong argumentation that gives us grounds to doubt the findings of science we also ought to remain open to the possibility that there could be strong argumentation that gives us grounds to conclude that we can know with complete certainty that your dog or Allen's scrap of tin foil does not control the world. In particular, transcendental argumentation of the sort discussed in this answer has a chance of showing just this.

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 the Seven Sanctified Sea Lions. Or, to take a more traditional example, maybe everything we see is planted in our immaterial minds by Descarte's Evil Genius.

Many philosophers would say that there's no way we can definitively rule such things out, but most of these same philosophers don't see that as a reason to worry. Substantive knowledge carries with it as a matter of logic the possibility that we might be wrong. But to quote once again my former colleague Dudley Shapere, there mere possibility of doubt isn't a reason for doubt. In other words, even though there's a bare abstract possibility that we might be wrong in all sorts of ways, that doesn't give us any reason to suspect that we are.

One way to approach the philosophical enterprise of making sense of knowledge is to see the project as proving that we actually know things. Another approach -- the more common one these days -- is to take it for granted that we know a good deal and look at the structure of the building from the inside. When we do that, we don't find much in the way of reasons to worry that Poochie rules the world.

As Saul's response makes clear, Descartes' own reasoning seems to rely heavily on his argument for the existence of God. I think that few today would accept that argument, and so although studying Descartes closely would doubtless be interesting it may not give you a satisfactory answer to your questions.

Another form of argumentation that purports to be capable of proving the existence of objects distinct from oneself is transcendental argumentation. This is most closely associated with Immanuel Kant, who developed his famous transcendental argumentation (at least in part) because he was interested in responding to problems with the rationalist philosophical tradition in which Descartes wrote and which was critiqued severely by David Hume.

As interesting as Kant's argumentation is--and as fascinating as is an historical account of Kant's responses to his illustrious predecessors--Kant's own argumentation may not help you to find an answer to your question: although Kant answered your questions directly and powerfully, his argument presupposes metaphysical positions that are hugely controversial and that few today would accept. So, although both Descartes and Hume thought that they had in hand answers to your questions, from a contemporary perspective most folks would find these answers unpersuasive.

Happily, however, Kant has inspired a series of additional transcendental argumentation, many of which are more palatable from a contemporary perspective and some of which may yet provide answers to your questions.

In schematic form, transcendental argumentation looks like this:

FIRST STEP: Start with a phenomena that everyone agrees exists (e.g., experience).

SECOND STEP: Investigate the necessary conditions for that phenomena by asking the “Kantian question” of what makes it possible.

THIRD STEP: Examine the philosophical implications of your analysis of the possibility of the phenomena.

Kant’s major insights included, first, that the necessary conditions studied in step two can have vital implications that can be exploited in step three and, second, that traditional rationalists and empiricists who do not use “Kantian transcendental arguments” are ignorant of these implications and so make many horrid philosophical mistakes.

In Kant’s case, he gave transcendental arguments about the possibility of experience, and from them he believed that he solved both the "crisis" about knowledge that Descartes' Meditations responded to and intensified and the Humean "crisis" about causation that was at the heart of Hume's criticisms of Descartes' positive account of knowledge.

To my reading, at least, contemporary versions of this "Kantian-style transcendental argumentation" are seen in the work of Donald Davidson, who asked how communication was possible (and who developed startling new theories of language, mind, and action when he explored the implications of the correct answer to that question); in the work of Jurgen Habermas, who asked how "communicative action" was possible (and whose answers helped him to develop an influential theory of social critique); in the work of Ludwig Wittgenstein, who asked how is language possible; by Wilfrid Sellars, who asked how are concepts possible; in the work of Peter Strawson, who asked how is it possible to know what someone else thinks; in the work of Hilary Putnam and John Searle, who each ask how is it possible for words to refer to things in the world; and in the work of many cognitive scientists, for example Owen Flanagan and Paul Churchland, who ask how is it possible to represent anything in the mind.

So, if I am right "Kantian-style" transcendental argumentation constitute a powerful source of contemporary philosophical insight, and studying Kant's arguments and relevant contemporary ones may therefore provide a rewarding way to engage deeply the issues that your question raises. the

Among the recent transcendental argumentation, I think that Donald Davidson offers the most direct response to the questions you raise. His arguments are difficult, but extremely interesting. Alas, they tend to be distributed throughout many different writings and so there is no single article that I can refer you to. A good starting place may be his "Epistemology Externalized," "Meaning Truth and Evidence," and "Three Varieties of Knowledge" each of which contains interesting material on this theme that Davidson published in the 1990s.

The fact that you're talking about Descartes and the cogito with a friend is an excellent start. It is certainly a main part of the project of Descartes' Meditations on First Philosophy to prove that one can have knowledge of a world which extends beyond one's awareness of oneself as a thinking thing. I would recommend a careful reading of that work, with particular attention to the third Meditation, where Descartes explicitly considers and rejects the suggestion you've hinted at, namely that the existence of a world outside oneself follows from the fact that the world seems to impose itself on us, often against our will. Descartes rejects this argument because it is possible that such ideas could still be invented by us, and only appear to issue from outside us. This point is made in preparation for the proof of God's existence in Meditation 3, where Descartes argues that when one reflects on the content of one's mind, only our possession of the idea of God requires that there be something outside oneself, namely God, who is the the cause of that idea. Once Descartes has established the existence of God, (if his argument is successful) he's on his way to showing that there are other things than God outside him. The culmination of Descartes' argument occurs in Meditation 6, where he argues for the existence of the external (physical) world.

It's not obvious what the argument is here. Are we trying to argue that we actually are just avatars in a computer simulation? If so, then the argument seems pretty weak. Are we trying to argue that we don't know that we're not avatars in a computer simulation? Then., again, one wants to know what the argument actually is. It seems to be something like: We can't absolutely rule out that we're not avatars, etc, etc. And if so, then, yes, I agree that Putnam's brain-in-a-vat argument is actually pretty hopeless. But my own view, for what it's worth, is that the BIV argument doesn't actually have anything to do with skepticism. (I think it has to do with metaphysical realism, a very different topic.) But the deeper question, I think, is whether knowing that p actually requires being able to rule out the bare possibility that not-p, and not everyone would agree that it does, especially where skeptical scenarios are concerned.

Have a peek, for instance, at Jim Pryor's paper "The Skeptic and the Dogmatist" or, for that matter, at G.E. Moore's paper "A Defense of Common Sense". Moore claims that he knows that he has two hands and, since it follows from the fact that he has hands that he is not an avatar---avatars don't have hands---it follows that he knows that he isn't an avatar. He agrees, to be sure, that he can't prove that he has hands---you can't prove anything, except in mathematics---Moore flatly denies that it follows that he doesn't know that he has hands. Which, indeed, it doesn't.

Philosophers will disagree about the details here. But I think many, maybe even most, philosophers nowadays would agree with the main point I've been making: Simply showing that, in some sense, it is barely possible that p shows nothing as regards anyone's knowing that p.