They were, however, all nice discriminators as to the class of case before them, and they knew well what danger there was in admitting to their "guild" any with a little more disgrace than their neighbors.
"The Fortunes Of Glencore"
Charles James Lever
Here are double doubts for the discriminators: their "sign of the infinitive" fails, or becomes uncertain; because they do not know it from a preposition.
"The Grammar of English Grammars"
Goold Brown