“Better to keep your mouth shut and be thought a fool than to open it and remove all doubt.” Makers 401

Why is clear thinking so often associated with clear speech?  Obviously one who has the capacity to be intelligent and has the gift of language would not be considered a fool but why do we automatically assume the most vocal to be the most worldly?  Why are speech impaired people called “dumb”?  In my experience the most intelligent people do little talking, they are often the ones who listen to what others are saying and perceive their conclusions many steps in advance.  I believe in many cases people who vocalize their ideas are sharing them in order to help themselves fully understand them and to offer them up for peer scrutiny which is not a negative exercise but if they fully understood the concept it certainly would not be necessary to externalize it.  I believe language is a knowledge refining process.  One has to filter ideas through language to be able to share it and interrogate it.  True knowledge does not have a dialogue; it merely exists and is utilized in its pure form, enacting itself without the mediator of language.  Some of the most intelligent people in the world cannot speak.  Are babies still human before they gain speech?  Are they any more intelligent after they’ve learned?