Your argument is:

(1) Our senses and perception are subjective.

(2) Everything we know is based on on our senses and perceptions.

Therefore

(3) Everything we know is subjective.

There is a well-known difficulty with this argument. It equivocates on "subjective". In the first premise "subjective" means something like the innocuous "possessed by a subject", but in the conclusion it is presumably taken to mean the toxic "not having any objective truth". There is also a doubt about the second premise. Many philosophers accept the idea of "a priori" truths, that is, truths that hold independently of experience, including mathematical truth and perhaps ethical truths, if there are any.

I suppose the worry your thesis and argument raises has to do with the meaning of "subjective" and the move that a given person's beliefs are based on the senses to the conclusion that "All truths are subjective."

On subjectivity: I share the view that persons do indeed have feelings, perspectives, opinions, senses, and perception. We might also add reason, memory, emotions and passion, interests, drives, and so on. When we do know things based on such states or processes (for example, I know I am awake and writing to you), is my knowledge itself something we would call subjective? I suggest we would want to say that it is objectively true or the case that I am writing to you, and not subjective in the sense that it is only true from my point of view or because I think it is true. So, paradoxically, I think that if we do want to claim that there are subjective states that they really exist then we are in effect committed to holding that the existence of subjective states is an objective fact about the world. The world or reality includes subjects who have subjective states.

On "All truths are subjective": While I think it is true that no person can assert that something is true without being in some mental state and thus in some state of subjectivity (e.g. Skippy believes that there are no people on the sun), it is not clear what it would mean to assert that "All truths are subjective." Presumably the truth that 'There are no people on the sun" does not depend upon anyone's subjective states.

This is an excellent question and one that is much debated historically and today. It has implications about freedom and determinism, logic, and the philosophy of God, good and evil. It seems that classical logic requires that propositions are either true or false. "Barack Obama is the forty-fourth president of the USA" appears to be a proposition. And we have found it to be true. But in that case, it seems that Obama could not have failed to have won the election against McCain. It has seemed to some (but certainly not all) philosophers that this would mean Obama's election was fixed in some sense, perhaps determined. Some who worry about this problem are theists who think that if God knows from eternity that in August of 2011 you would ask your question, then there is no possibility that you would not have typed in and submitted your question to Askphilosophers. For many theists, it is vital to affirm that creatures / human beings have free agency, otherwise it would seem that God has determined humans to be evil. The other worry about what is called future free contingents (the fancy term for propositions that refer to future events that appear to involve freedom and contingency) has to do with whether there even could be such future propositions. It seems that for a proposition to be true there must be SOMETHING in virtue of which the proposition is true. But in the 19th century, Obama did not exist; he did not exist then, nor was he existing in the 21st century. From this line of reasoning (which was probably Aristotle's), we should hold that propositions involving future free contingents are neither true nor false. Theists who take this position (like Richard Swinburne) contend that even an omniscient God does not know about future free continents. According to Swinburne, God knows all possible truths and because propositions about future free contingents is neither true nor false and thus cannot (by definition) be known by any being of any kind, such propositions about the future are not the sort of thing that even God knows.

"Private," Hobbes writes in Leviathan, regarding the nature of beliefs, "is in secret free." These words are, I think, absolutely correct, and pertinent in the context of your excellent question, regarding whether agents have a right to hold whatever beliefs they wish, and whether other agents--and maybe even the state--have a right to correct those false beliefs. Hobbes's point is that the state need not concern itself with agents' beliefs, provided that those beliefs are not made publicly manifest; similarly, insofar as agents' beliefs do not interfere with the lives of others, then the state, and indeed, most other agents, have no right to try to change those beliefs. I am inclined to think that this point is broadly correct, since I'm inclined to favor minimal state interference with individuals. There is a question, however, whether agents have an epistemic duty to try to achieve true beliefs. This topic was the subject of an exchange between William James and W. K. Clifford, in which Clifford maintained that agents had an absolute duty to proportion their beliefs to the evidence, and James demurred; the basis for this disagreement was different conceptions of the point of belief. If one thinks that belief aims at the truth, an agent who does not even seek to achieve the truth may not even count as a believer, or at the very least, not a responsible believer; if, however, one holds some alternative conception of the nature and aim of belief, then one might not think that beliefs do indeed need to aim at truth. But what is it to believe something? This question, which has gripped philosophers interested in the theory of knowledge--epistemology--from Plato to the present, and in order satisfactorily to resolve your question, one needs to come to terms with it.

Descartes sought certainty because he thought that if we know something with certainty, then it must be true. And he was right, if only because 'S knows that p' implies p, so that in 'We know with certainty that . . .' the phrase "with certainty" is redundant; there is no such thing as uncertain knowledge. I suspect that the sense of your question may be Cartesian: is it the case that certainty implies truth? There are several concepts to sort out here: 'We know for sure, or for certain, or with certainty that . . .', 'I am certain (sure) that . . .', 'I feel certain, sure, that . . .', 'It is certain that . . .' (but not 'It is sure that . . .') There is a very useful paper by G.E. Moore called "Certainty" that might be helpful here, which is sensitive to distinctions of this kind. Sean is right in his response above that psychological certainty or "feeling certain" may not be a mark of truth, though I wonder whether anyone has troubled to test the correlation empirically in humans, and whether it makes sense to think about testing it in animals. On the other hand it also seems correct that if something is indeed certain, e.g. that 7×9 = 63, then '7×9 = 63' is true.

I presume that in asking whether certainty suggests or indicates truth, you mean whether an agent's certainty about some proposition is a mark of its being true. If this is correct, then in order to answer the question, one needs to get clear about the kind of certainty at issue. It certainly does not seem to be the case that an agent's psychological certainty, or confidence, in some proposition, is a mark of its truth, since one can be confident about the truth of some proposition that isn't true. If the proposition, by contrast, is certain--if, for example, the proposition is a necessary truth, or a proposition that is the object of what Descartes in the Meditations calls the 'natural light', or reason, and hence can be said to be metaphysically certain, then the certainty of the proposition would indeed be a mark of its truth. It seems to me, however, that the propositions that we, as epistemic agents, are most interested in aren't metaphysically certain--_pace_ Descartes, I fear that we lack a 'natural light' that yields metaphysical truths about the nature of the mind, God, and the material world--but are contingent truths; since I don't think that one can infer from one's certainty about some proposition that it is true, as mere psychological certainty does not seem to be a mark of truth, it would seem that certainty should not be taken as a substantial mark of truth.

In order to determine what role, if any, religion generally should play in knowledge about "how things are or came to be," it is essential first to know just what 'things' are at issue. For example, it seems to me that if the 'things' in question are truths about morality, then religion generally may well have a role to play; by contrast, it seems to me that if the 'things' in question are truths about the nature of the physical world, say, then it's not clear to me that religion has any role whatsoever to play in helping us to gain knowledge of such truths. (I write here not from any particular standpoint on the issue: indeed, even the great seventeenth-century French philosopher and theologian Nicolas Malebranche, who famously believed in the truth of occasionalism, the view that God is the only real cause in the universe, and, hence that all changes in the universe were effected by God's causal power, did not think that appeals to God were relevant in the context of giving scientific explanations. "One would make oneself ridiculous," Malebranche writes in his first, and to my mind, greatest and most philosophically significant work, The Search After Truth, "if one said, for example, that it is God who dries roads, or who freezes the ice in rivers. It must be said that air dries the earth, because....and that the air or the subtle matter freezes the river in winter, because in this time....In a word, the natural and particular cause of the effects in question must be given, if it is possible.")

Great question. I use a similar question on my first day of my Intro to Philosophy class to help my students see that not all questions have either objective answers or subjective answers. (I use "What is the greatest rock band of all time?" to make the point.) Objectively answerable questions are ones for which we have agreed-upon methods for finding a single correct answer: Is earth bigger than mars? How many humans are in this room? What is the capital of Nigeria? ... even if we don't yet know the answer: How many planets in the Milky Way have water on them? What will I weigh at noon on Jan 21, 2012?

Subjectively answerable questions are ones that depend only on the opinion of the person answering the question: What's your favorite color? What is your favorite rock band? What is your favorite soccer team?

But what about: What is the best rock band of all time? What is the best national soccer team in the world right now? (or: Why does Hamlet wait so long to avenge his father? What led to World War II?) These questions do not seem to be objective, nor subjective. I call them normatively answerable. By that, I just mean that we have norms about what counts as better and worse answers and also norms about what counts as better and worse ways or methods of answering them, though these methods may not point to a single correct answer. We also expect people to offer justifications for their answers to these questions and we make judgments about whether their justifications are defensible, irrelevant, etc.

The Beatles and Rolling Stones are defensible answers. Back Street Boys and In Sync are not. (Of course, the best answer is Led Zeppelin, which I can defend some other time.) Spain is a very defensible answer to what is the best soccer team. Alas, the USA is not. We could provide justifications both for the specific answer and for the methods we use to obtain it.

Here's a defensible method: The reigning champion of the World Cup is the best national team (especially if it is also the reigning European champion). So, Spain. But there are other defensible methods, including ones that use statistics (win/loss/tie ration, possession percentage, goals for/against, etc.). Without looking them up, I'd guess Spain is best on just about any of these measures. So, at this point the answer to this question may be easier than at other times.

Note that if the relevant community comes to complete agreement about how to answer a question, it looks objective. What is the best movie of the year? If we all agree it's the winner of the Oscar, then the answer is objective. But typically, we have lively debates about what methods are best to answer such questions, so they remain 'normatively answerable.' (I think most, if not all, ethical questions are normatively answerable.)

I hope this helps. And I hope that someday the US might be the best answer to the soccer question, but it might take a while.

t does not seem to me that appeals to this principle are based on induction--although there may well be cases in which the appeal is so based, and, consequently, I think that case studies of the extent to which this principle is applied, and when it is applied, on what basis, would be very interesting and most illuminating. It seems to me to that appeals to this sort of principle rest on one of a variety of methodological--or one might even say, metaphysical, presuppositions, of which I give a couple of examples: (i) a principle of epistemic parsimony or conservatism, that one should not multiply theoretical entities unnecessarily (sometimes called 'Ockham's razor') and that, consequently, one should prefer simpler to more complicated explanations when all else is equal; (ii) perhaps in conjunction with (i)--although they need not be conjoined--an assumption that the phenomenon in question ought to be simple, because the phenomenon is an instantiation, say, of a divine plan (cf. Einstein, "God does not play dice"), or because nature is simple (an assumption that strikes me as unwarranted), and so a hypothesis meant to apply to nature ought also to be simple as well.

Here's one way to respond. If one were to suppose, with Kant, that human dignity is intinsically valuable, and that lying to another--even if that lie would promote the other's happiness, say by sparing that person a harsh and painful truth--does not respect that person' dignity, by failing to--in Kant' terminology--treat that person as an end-in-itself worthy of respect--then one might therefore conclude that one has a duty to tell others the truth, and, since, again according to Kant, duty does not admit of exceptions, one cannot compromise that duty in any cae whatsoever, regardless of the consequences of so doing.

Of course, this response presupposes some very strong claims about the nature of human beings and the significance of duty. Implicit, too, is the assumption that morality is more intrinsically valuable than happiness. This is not to say that Kant, or a Kantian, wouldn't recognize the significance of promoting the happiness of others--if I remember correctly, Kant does so, explicitly, in Groundwork 1--but rather that the demands of duty, for Kant, take precedence over promoting the happiness of others.

If, by contrast, one took the maximization of happiness as the basis for deciding which acts are permissible, one might have reason to tell a lie in order to promote the happiness of another. (Although it's not clear that in the case under consideration, even a utilitarian who takes as her ultimate end the maximization of happiness would endorse lying. Her reasons for so doing, of course, would differ significantly from that of the Kantian, and, I must confess that I find the Kantian approach more intuitively attractive than other alternatives.)