The double space between sentences is a throwback to the era of typewriters. With sophisticated computer applications like Quark XPress this practice is no longer necessary and can cause text to look unprofessional. The simple answer is to type 2 spaces. This is referred to as word spacing.
To create double spacing between lines: select the text to double space, hold down Command (Apple), Option(alt), Shift on the keyboard. Then click the single quote key (') to increase space or the semi-colon key ( to reduce space between lines. This is referred to as leading or the space between each baseline of text. Simply select all text and input the leading number as double the point size of the text. For example, 12 point text with 24 point leading looks like a double return, or double space.
The above keyboard commands allow one to increase the space between lines quickly and 'globally'. For an editor / publisher / reader the text does not have to be exactly double spaced to the last degree to look presentable.
When speaking of formatting text one needs to be specific, there are 3 different aspects used to space text. Word spacing, leading and kerning (the space between letters).
This post has been edited by CosmoGozmo: May 25 2012, 11:01 AM