A world that has only periods is a world without inflections. It is a world without shade. It has a music without sharps and flats. It is a martial music. It has a jackboot rhythm. Words cannot bend and curve. A comma, by comparison, catches the gentle drift of the mind in thought, turning in on itself and back on itself, reversing, redoubling and returning along the course of its own sweet river music; while the semicolon brings clauses and thoughts together with all the silent discretion of a hostess arranging guests around her dinner table.
quoted from a Time Magazine Article by Pico Iyer, In Praise of the Humble Comma