Attempting to describe the language you speak is about as difficult as attempting to describe yourself as a person. Your language is very much part of you and your thinking. You use your language so instinctively that it is difficult to stand outside yourself and think of it as something that is independent of you, something which you know and which can be described. You may even feel inclined to say that your language is not something you know, you just speak it, and that’s all there is to it. But as the native speaker of a language, there is an important sense in which you do know all that there is to know about that language. This is not to deny that there are almost certainly words with which you are not familiar. Perhaps you don’t know the meaning of the word lagophthalmic. If so, your (understandable) ignorance of this is more medical ignorance than ignorance about the English language, and is anyway quickly remedied with the help of a dictionary. But there is much more to a language than its words. There is much more that you do know about your language which cannot so conveniently be looked up, and which you were never explicitly taught. And this is knowledge of a more fundamental and systematic kind than knowledge of the meanings of individual words. The more fundamental such knowledge is, the more difficult it is to become consciously aware of it.