This is a question that is frequently asked, or thought of, even if it is not verbalized, by my clients. The lawyerly answer is because language is an imperfect medium to describe complex thoughts, ideas, and meanings. There are vagaries to every word, and every sentence written. However, a better way to explain it may be through an example.
New legislation is passed to protect city parks. As a part of that legislation a sign which reads “No Vehicles in the Park” is put up. Now most people, on the surface, would be happy with this. It is a simple sentence, devoid of legalese, and defines its purpose. However, think about where the ambiguities come into play.
Are Cars allowed in the park? Certainly Not
Bicycles? Maybe not
Skateboards? Maybe not
Wheelchairs? Again, Maybe Not
Was the intention to prevent Bicycles and skateboards? or just automobiles, ATVs, and Motorcycles?
Do we say “No Motorized Vehicles in the Park”?
Does this prevent motorized wheelchairs as well?
What about kids scooters with little trimmer motors on them?
What about remote control cars?
While this example is taking literal language a bit to the extreme, I think it is an effective way to illustrate the point that an intention as simple as keeping cars out of a park, and a sentence as simple as “No Vehicles in the Park” can create so much argument and ambiguity. Imagine applying this to the business context, where each party is going to be seeking to get as much gain as possible from the deal, and you can start to understand why contract provisions need to be so explicitly clear as to what is included and what is not. The key component of a contract is its preciseness: It means what it says and says what it means. So, next time your attorney is drafting a contract, and you wonder why it has to sound so complicated, think about how many different ways the language could be interpreted if it was not so explicit.