According to Vim's manual:
A sentence is defined as ending at a '.', '!' or '?' followed by either the end of a line, or by a space or tab.
However ( and ) normal-mode motions seem to have no effect if there's only one space between sentences:
First sentence. Second sentence. But ( and ) work as expected if there are multiple spaces between sentences:
First sentence. Second sentence. My question is why ( and ) have no effect when sentences are separated with a single space?
set nocpto your .vimrc