I’m reliably informed that in the days of typewriters. it was always customary to insert two spaces after a full stop. And it is still my instinct to leave two spaces. But the grammar check in Word defaults to only one space.
However, after some research, I worked out that Word allows you to set the number of spaces between sentences (Options/Proofing/Grammar Settings). You can also tell it not to check this aspect (which I have now done).
But, more generally, the topic of spaces between sentences even has a Wikipedia entry! That states, “The desired or correct sentence spacing is often debated but many sources now say additional space is not necessary or desirable”. The article sets out the issues at some length, and it seems that in some quarters strong views are held on the matter. I thought my views were just a little quirk on my part, but it seems I’ve touched on what for some people is a serious matter!
Musings and Mutterings 