Spaces between sentences

     [This is a fast-access FAQ excerpt.]
This issue is more suited to comp.fonts than here.  In recent
years, printers typesetting with proportional fonts have generally
*not* made the inter-sentence space any greater than the inter-word
space, although greater inter-sentence space can be found quite
often in older books.  Traditionally, students in typing classes
have been taught to put two spaces between sentences.  Some people
never like the extra space, some always do, and some like it if the
text is monospaced but not if it is proportionally spaced.  The
traditional UNIX text formatter, troff, uses extra space; in TeX it
is optional, but turned on by default.  The extra space, if used,
need not be as much as the normal interword space (it can be less in
TeX, but not in troff).  Advocates of the extra space argue that
the practice speeds reading by making it easier to pick out
sentences.  And sometimes it can aid clarity.  A passage such as:
| "What's pluperfect?" is a reasonably reasonable question that has
| yet to be sweetly but fully answered on a.u.e. I answer the
| questions about Erzherzoginen (Habsburg archduchesses).
is far from clear on first reading.