First of all, huge question. Many a thinker have attempted to sort out this question and pose possible answers to it. The main issue your question deals with is the Subjectivity of one's own perceptions. Without getting into too much detail, my answer to your question relies heaviliy on pragmatisim. Just imagine a world where a human being's perceptions were hugely different from anonther's. Could society really function at all? Of course not. Our obvious ability to communicate with one other about our perceptions stands as evidence in the objectivity of our perceptions. The clearest example is in our use of indexicals (Words like: now, here, there, and this.) We can use these words to communicate with each other with astonishing presicion. For example, say you and I were together and both percieved an object. This object is nothing like we've ever seen before, something completely foriegn. I, without giving a description of the object, simply point my finger at it and say "Hey, look at that!". Undoubtedly, you will understand what I'm talking about. I hope my comment helps.