The book is primarily concerned with natural languages that function as fullfledged
mother tongues for larger or smaller groups of people. It is less concerned
with the clearly artificial and highly restricted languages of, for instance,
mathematics, formal logic or computer programming. The line of division is not
always clear. While the word one belongs to English, the number 1 belongs to
mathematics; and while the words if and then belong to English, the logical operator
if-then belongs to formal logic and computer programming.