Why is it so hard to pin someone down to an agreed interpretation of what a particular phrase or sentence means? […] Language is not intended for debates. For pre-Darwinian philosophers like Descartes, who believed that language was designed and delivered to humans by a divine power, this must have been almost impossible to understand. Only when we recognize that language is a human invention, designed for a specific purpose, can we see that there are some things which language just can’t do.
Here’s a simple example: imagine there are two types of fruit tree that grow on Mars. They look completely identical, but one smells of oranges and the fruit is instantly fatal: the other smells of lemons and the fruit is sweet and healthy. A party of starving explorers gets in touch with you by radio and asks for your help in determining which fruits they can eat. The only problem is that they grew up on Venus and have never smelt either an orange or a lemon before.