 One of the most popular arguments against wider sentence spacing is that it was created for monospaced fonts of the typewriter , and is no longer needed with modern proportional fonts . However , proportional fonts existed together with wide sentence spacing for centuries before the typewriter , and remained for decades after its invention . When the typewriter was first introduced , typists were most commonly taught to use three spaces between sentences . This gradually shifted to two spaces , while the print industry remained unchanged in its wide em @-@ spaced sentences . Some sources now state it is acceptable for monospaced fonts to be single spaced today , although other references continue to specify double spacing for monospaced fonts . The double space typewriter convention has been taught in schools in typing classes , and that remains the practice in many cases . Some voice concerns that students will later be forced to <unk> how to type . 
