Many years ago someone asked a question I'm still unable to answer. I think it falls under 'perception'. I traveled quit a bit and had many interesting experiences as a woman working for a multi-national corporation. While in Pakistan, I met a co-worker's wife. We got along very well and had a great time discussing something we both enjoyed very much - cooking. She turned to me and asked, "What does an avocado taste like?" They just weren't available to her in Lahore. She had seen pictures and read recipes but never had one.
I couldn't relate the taste through comparison because avocadoes are unique. I could talk about colour or texture but that didn't satisfy her question about flavour. I asked many people when I got home. The answers all related to texture or colour. I had an interesting disagreement over the answer, "It tastes green." How do you express or talk about flavour without a base to compare against? How can someone share perception without a common experience?
That's a great example, and a great question. There are a number of obstacles to conveying the taste of an avocado to another person in words. Some are practical and some are philosophical. First, even those of us who've tasted avocados will have difficulties recalling the taste when we're not actually tasting it. I bet I could do pretty well distinguishing avacados from other substances in a blind taste-test, but my current acquaintance with the taste is not so determinate right now as I sit in my office trying to conjure it up while drinking water. I would have an easier time describing the taste to your friend if I were currently eating an avocado. Second, we seem to have no "purely qualitative" language for picking out the way things taste to us "from the inside". By this I mean that all the descriptions we might use seem to make inelimanable reference to some external substance, and then draw comparisons with the taste it typically causes. Even "salty" means something like "tastes similar to...