Every normal person in the world, past infancy in years, can and does talk. By virtue of that fact, every person — civilized or uncivilized — carries through life certain naive but deeply rooted ideas about talking and its relation to thinking. Because of their firm connection with speech habits that have become unconscious and automatic, these notions tend to be rather intolerant of opposition. They are by no means entirely personal and haphazard; their basis is definitely systematic, so that we are justified in calling them a system of natural logic — a term that seems to me preferable to the term common sense, often used for the same thing.