GrandFather,
From the readme - Plurals of "uncountable" nouns were included, annotated with the "%" suffix character. See below for an extended discussion of the inclusion of these words.

Keep in mind that 2of12.txt ne 2of12inf.txt though I am thinking for add-ons to the challenge, UK english as well as inflections will add to the complexity though the techniques should remain relatively the same.