http://xkcd.com/1028/ The alt-text (discovered when you hover your cursor over the comic) is particularly relevant.
Clarity is in the final comprehension, as the proof of pudding is in the eating. Clarity is not about being able to be understood, or even about being so clear as to not be misunderstood: it is about actually being understood.
Legal writing is meant to be clear, but it is famous for being confusingly unclear. By being overly specific, general meaning is lost. Legal writing is difficult because it tries to address two audiences: the earnest, non-technical crowd who only wants the general meaning and idea, and the conniving, dastardly, sneaky crowd who looks for any slight ambiguity to exploit for gain.
Our common language utilizes non-specificicty and ambiguity as a sort of social lubricant, allowing conversations to flow along and meaning to be conveyed lightly. When lawyers write even simple things, they do so expecting every possible contest of even the most basic statement.
People ask the fair question: “Why can’t lawyers just write simply so we can understand?” One reason is that understanding is not entirely dependent on the words; a lot of understanding is gleaned from context, situation, and background understanding. The awful writing of lawyers shows what communication would be like if we were robots and not humans. Cultural shorthand allows us to communicate ideas without pinpoint specificity- but we experience confusion when unspoken background assumptions do not overlap quite right. When communication is a product of working together with a common background and a common goal, the language can be imprecise and simple. When communication occurs in anticipation for a battle, with different aims and understandings, the language must be as excruciating and as tortured as the human relations it symbolizes or indicates.
Lewis Carroll’s conversation between Humpty Dumpty and Alice questioned whether it was the same thing to “mean what you say” as to “say what you mean.” I think that common language is when we mean what we say. When we attempt to “say what we mean,” we find we wax verbose, place many qualifiers, modifiers, and all sorts of limitations on every clause and term. It is a very difficult thing to say precisely what we mean—no more and no less. It may be an impossible task to communicate on both the cooperative and competitive levels.
Writing can only have value if it is read and understood.