Ancient manuscripts were written continuously, thus:

ONEWORDFOLLOWEDANOTHERCLOSELY.

Later the words were separated by spaces, and sometimes by dots and other marks. The punctuation marks now employed have come to be used with so much definite-ness that they are a great help in enabling us to express our meaning exactly. They not only assist us to present one thought at a time, but they also help indicate the relation between words expressing a thought. The marks most often used in ordinary writing are: the period (.), the comma (,), the colon (:), the semicolon (;), and the dash ( - ). We should be careful to have a reason for every mark that we use.