قد تُحلّ في الدراسة مسائلُ حيّرت كلَّ من حاول حلّها بحواسّه. غير أنّ بلوغ هذا الفنّ أعلى ذراه يقتضي أن يكون المستدلّ قادراً على استعمال كل الوقائع التي بلغت علمه؛ وهذا يعني، كما ستدرك بسهولة، امتلاكَ المعرفة كلّها، وهو أمرٌ نادرٌ حتى في هذه الأيام التي يسّرت فيها التعليمُ المجانيّ والموسوعات.

“Problems may be solved in the study which have baffled all those who have sought a solution by the aid of their senses. To carry the art, however, to its highest pitch, it is necessary that the reasoner should be able to use all the facts which have come to his knowledge; and this in itself implies, as you will readily see, a possession of all knowledge, which, even in these days of free education and encyclopaedias, is a somewhat rare accomplishment.”Arthur Conan Doyle — The Complete Sherlock Holmes (Illustrated): All 4 Novels and 56 Stories with More Than 480 Illustrations (2014)