If you take the sixth sense analogy seriously, the next step is to ask why you believe the other five senses. The answer is not "because I understand how they work." To begin with, you probably don't, and even if you do, Aristotle certainly didn't--and none of us are willing to argue that he ought to have denied the evidence of the senses.You believe your five senses because you have imposed on them all the consistency tests you can think of, and they have mostly passed. You see something, your eyes tell you an object is there, you reach out and sure enough you can touch it. The thing is a bell. Last time you tried hitting a bell your ears told you there was a sound; you try it again and it still works. Occasionally there is an apparent contradiction--you can't touch a holographic image, and when you hit a holographic image of a bell it doesn't make a noise. But as you get farther and farther into the structure of the physical world revealed by your senses more and more of those contradictions turn out to make sense after all.A second set of tests occurs to you. Your senses tell you that other people are very much like you. If so, they should perceive the same physical universe. You ask them, and sure enough they almost always do--again with very rare exceptions such as color blindness, exceptions that turn out, on further examination, to make sense. Note, however, that what you are finding to be consistent is observation of very primitive facts--there is a table there, there is not a lion sitting on the table. About the patterns implied by those facts--for example, whether capitalism or socialism results in higher standards of living, or whether the earth goes around the sun or the sun around the earth, or whether paying enough money to the Church of Scientology will turn you into a superman--there is lots of disagreement. You conclude that your senses give you a reasonably accurate picture of the base facts of physical reality, consistent with that of almost everyone else, but that reasoning up from there is sufficiently hard, and/or depends sufficiently on the particular subset of facts observed, so that people disagree a good deal--and your confidence about your beliefs on that level should be appropriately weaker. You accordingly conclude that the physical universe is really out there, and the parts you have observed really have about the characteristics you observe. If someone tells you that there is a lion on the table you conclude he is a lunatic. If he is very convincing, you ask a few other people first and then conclude he is a lunatic.Now apply the same approach to moral reality. Replace sense perceptions with moral judgements--not grand theories such as "you should never violate rights" but "perceptions" such as "in the following well described situation, person X acted wrongly." Checking with other people you find, pace the ethical relativists, a very high degree of agreement. The disagreement either involves the sort of situation that, on consideration, you find morally difficult or (far more often) disagreement about the assumed facts, not the judgements.