An em space is the width of the letter m. IIRC, a normal space in most proportional fonts is closer to the letter n.
It has always been my understanding that historically, typographers tended to prefer em spaces between sentences (vs. after intra-sentence punctuation like 'Mr.' or a comma). And so, once typewriters with their fixed-width fonts came out¹, people used a double-space at the end of a sentence to approximate an em space.
The frustrating thing, typographically-speaking, is that the HTML approach doesn't map to the manually-typeset process, either, since it doesn't have any semantic knowledge about "end of sentence" vs. "random intra-sentence punctuation" and thus treats them all the same.
(Note that this is also where we get em dashes and en dashes from. And just like em spaces and en spaces, an em dash is transliterated to '--' in fixed-width fonts.)
¹ For all I know, the double-space trick was used with fixed-width letterpress before the advent of typewriters. The problem seems to have more to do with fixed-width than with typewriters.
Dylan16807|12 years ago
pcl|12 years ago
It has always been my understanding that historically, typographers tended to prefer em spaces between sentences (vs. after intra-sentence punctuation like 'Mr.' or a comma). And so, once typewriters with their fixed-width fonts came out¹, people used a double-space at the end of a sentence to approximate an em space.
The frustrating thing, typographically-speaking, is that the HTML approach doesn't map to the manually-typeset process, either, since it doesn't have any semantic knowledge about "end of sentence" vs. "random intra-sentence punctuation" and thus treats them all the same.
(Note that this is also where we get em dashes and en dashes from. And just like em spaces and en spaces, an em dash is transliterated to '--' in fixed-width fonts.)
¹ For all I know, the double-space trick was used with fixed-width letterpress before the advent of typewriters. The problem seems to have more to do with fixed-width than with typewriters.